special issue

physicsworld.comQuantaFor the recordThe possibility for discovery is offthe chartNobel laureate Sam Ting quoted in the ObserverTing’s $300m Alpha Magnetic Spectrometer,which will attempt to discover the origin of highenergycosmic rays, will finally get a trip to theInternational Space Station towards the end of theyear on one of the final Space Shuttle launches.It is very difficult; it is really difficultNASA boss Charles Bolden talking to the BBCBolden was close to tears during an interview whenasked to reflect on his time as an astronaut and todescribe what it means to him to witness the endof the shuttle programme, which has run for morethan 30 years.It is extraordinary that this action hascost £200 000 to establish themeaning of a few wordsScience writer and physicist Simon Singh quotedin the GuardianSingh penned a comment piece for the Guardian inApril 2008 criticizing the British ChiropracticAssociation (BCA) for claiming its members coulduse spinal manipulation to treat children with earinfections, asthma and other ailments. The BCAthen sued him for libel denying these criticisms.Last month Singh won the right to use “faircomment” in his defence.It is a very low bar – there is basicallyme and Patrick MooreParticle physicist and broadcaster Brian Coxquoted in the Daily MailCox, who came 70th in People magazine’s100 sexiest men of the year, comes over allmodest when praised for being “good-looking…fora scientist”.I have never forgiven them – myGerman is still pitifulQueen guitarist Brian May quoted in EurekaMay, who finally completed his PhD inastrophysics in 2007, still regrets being forced tostudy German at school on the grounds that itwould help him to understand physics papers byGerman researchers.They have been a breath of fresh airEnvironmentalist James Lovelock quoted inThe TimesLovelock says that climate sceptics have kepteveryone from regarding the science of climatechange as a religion.Physics World May 2010Seen and heardThe jokes are on CERNWith the Large Hadron Collider (LHC)having just recorded it first high-energycollisions, the CERN particle-physics labnear Geneva was, perhaps not surprisingly,the main focus of last month’s physicsbasedApril fool gags. The Independent,rather lamely, claimed that a successor tothe LHC – dubbed LHC II – was earmarkedto go in the 23 km circumference Circle lineof the London Underground. Meanwhile,technology website CNET UK announcedthat a man had been arrested at the LHCafter having travelled back in time to tryand prevent the collider from starting upand destroying the world. Keen not to missout, a CERN press release noted the LHChad made its first discovery since it collidedprotons at 3.5 TeV per beam on 30 March.The release claimed that two researchershad found a paleoparticle, nicknamed“neutrinosaurus” because of its“prehistoric origins”. Yawn. Possibly thebest April fool was by physicistAdam Falkowski from Rutgers University,who announced on his blog Resonaancesthat the “unmistakable” tracks of asupersymmetric particle had been foundby the ATLAS detector at CERN. At leastone Nature reporter fell for the gag anddouble-checked with CERN if thediscovery was true. Now that is funny.Physics à la carteThe culinary limit of most universityphysics students is probably beans on toast,with, if they are feeling especially creative,a splash of chilli sauce on top. But studentsat Harvard University might be rustling upsomething much more exciting in thefuture. This autumn the renowned chefFerran Adrià, from the world famous,three-Michelin-starred restaurant El Bulliin northern Spain, will begin teachingculinary physics at the university. Over a13-week term, Adrià will team up withfellow Spanish chef José Andrés to helpstudents get to grips with the requiredparameters to make a decent dish.ABC Transport for London 2005Students on the course can look forward todemonstrations from the chefs on, forexample, how to make bubbles of airsurrounded by a thin sheet of fluid, whichare the inspiration for Adrià’s specialityfoams of beetroot, mushroom andexpresso. Whether Harvard students willnow be rustling up Adrià’s signature dishes– intertwined carrot chips with lemonverbena, ginger and liquorice followed bymelon caviar – remains to be seen.Lambs for the chopIf you read the Sun, then you might beforgiven for thinking that the laser is not ahuman invention. According to a report inthe paper last month, some UK farmersnear Shrewsbury believe that advancedalien civilizations have been using lasers toattack their sheep. Former steelworkerPhil Hoyle, who has spent a decadeinvestigating unexplained livestock deathsin the area, says the attacks are beingcarried out by two orange-coloured spheresthat zap the sheep and remove their brainsand eyes. “The animals are being clinicallyand surgically sampled by a highlyadvanced technology,” an alarmed Hoyletold the newspaper. Having interviewedfarmers, he notes that “all but one” hadexperienced the disappearance or strangedeath of one of their animals. Hoyle offersno explanation for the aliens’ prowess withlasers but says that the devices must be built“by technology and intelligence that’s notfrom here”. The mystery continues.Buzz offHe may have been thesecond man to step on theMoon, but Buzz Aldrinprobably spent more timeon the lunar surface thanhe did on the US TV showDancing with the Stars.The 80-year-old former astronaut becamethe second celebrity to be voted off theshow last month and recorded the week’slowest score from the judging panel.Despite training for five hours a day beforehis stage debut, Aldrin gained only13 points out of 30 for his waltz, which heperformed with dance partner Ashly Costa.However, Aldrin’s appearance had anulterior motive – to promote the US spaceprogramme and its future direction.“[I did] the best I could to spread interestamong Americans and the rest of theworld about the achievements of successthat I was a part of in the past,” he toldEntertainment Weekly.3

physicsworld.comFrontiersIn briefElement 117 createdScientists in Russia and the US have created a newelement with 117 protons by firing calcium-48ions at a target of berkelium-249. Although nuclearphysicists had previously synthesized a total of27 elements heavier than uranium, element 117had remained elusive because the target materialneeded to produce it – berkelium-249 – is sodifficult to make. The researchers managed,however, to produce 22 mg of it by intense neutronirradiation over two years, which they then firedcalcium-48 ions at over a 150 day period. The newelement is the most neutron-rich isotope yetproduced, but its half-life of 78 ms is 87 timeslonger than a previously discovered isotopecontaining one neutron less. This supports the ideathat neutron-rich superheavy nuclei could beextremely stable (Phys. Rev. Lett. at press).Gravitational waves within sightFluctuations in the curvature of space–time knownas gravitational waves could be discovered within ayear of current detectors being upgraded, providedthat the detectors focus their search on emissionsfrom binary black holes. That is the view ofastrophysicists in Poland, who believe there aresignificantly more of these astrophysical systemsthan was previously thought. After analysing datafrom the Sloan Digital Survey, the researchersfound that 50% of stars in a sample of 300 000galaxies have a lower “metallicity” than the Sun,which makes them much more likely to formblack-hole binaries as they lose less mass at theend of their lives. Upgrades to the LIGO and VIRGOexperiments, to be completed by 2015, should givethem the sensitivity to detect these gravitationalwaves “within the first year of operation”, claim theresearchers (arXiv:1004.0386).Wonder material steals the lightResearchers at IBM have made the firstphotodetector from graphene – a sheet of carbonjust one atom thick. Photodetectors convert opticalsignals into electrical current and they are widelyused in communications and sensing. Theresearchers needed to overcome a rare flaw ingraphene: the electrons and holes in the bulk ofthe material recombine too quickly, which leavesno free electrons to carry current. They applied aninternal electric field via palladium or titaniumelectrodes that are on top of multilayered orsingle-layered graphene, which separates theelectrons and holes. The graphene photodetectorcan detect optical data at rates of 10 Gbit s –1 ; thiscompares well with optical networks made of othermaterials, such as group III–V semiconductors(Nature Photonics 10.1038/nphoton.2010.40).Read these articles in full and sign up for freee-mail news alerts at physicsworld.com4Strange quark weighs in preciselyElementary stuff “Strange” quarks are the heaviest ofthe three light quarks.A collaboration of particle physicists inEurope and North America has calculatedthe mass of strange quarks to an accuracy ofbetter than 2% – beating previous results bya factor of 10. This is the first time that themass of one of the lighter quarks has beenconstrained to such accuracy and could helpexperimentalists to scrutinize the StandardModel of particle physics.It is notoriously difficult to determine themass of quarks because these elementaryparticles never exist in isolation – instead thestrong force constrains them into boundstates called hadrons, such as the proton andthe neutron. The picture is complicated be -cause a large portion of the hadron mass isbelieved to belong to the strong force itself,mediated by particles known as gluons, andthe exact nature of gluon–quark interactionsis poorly understood. Theorists thereforehave to combine measurements of hadronI spy quantum behaviourPhysicists in the US have observed quantumbehaviour in a macroscopic object largeenough to be seen with the naked eye – a thindisc-shaped mechanical resonator measuringabout 6.25 mm × 6.25 mm and consisting ofaround a trillion atoms. In making their ob -servations, Andrew Cleland and colleaguesat the University of California, Santa Barbara(UCSB) have exploited one of the fundamentalprinciples of quantum mechanics –objects being in two states at the same time.To achieve these “superposition states”,an object needs to be cooled down to itsquantum ground state, at which point theamplitude of its vibrations is reduced to closeto zero. Until now, such states have onlybeen induced in objects up to the atomicscale and some larger molecules, such as“buckyballs”, which are made up of 60 carbonatoms. However, the temperature towhich an object needs to be cooled in orderChristine Daviesbehaviour with calculations based on quantumchromodynamics (QCD), the theory ofthe strong force, to define the mass of singlequarks. Refinements to this theory over theyears have enabled physicists to calculate themass of the heavier three quarks – the top,bottom and charm – to an accuracy of 99%.Unfortunately, it is has been much more difficultto make accurate predictions for themass of the three lighter quarks – the up,down and strange – so reference tables stillcontain errors of up to 30%.Christine Davies at the University of Glas -gow and colleagues in the High PrecisionQCD Collaboration have, however, takena different approach, known as “latticeQCD”. The technique, which requires theuse of supercomputers, enables theorists toconfine the highly nonlinear strong interactionby defining quarks as nodes on a gridand gluons as the connecting lines. Davies’team adapts lattice QCD to calculate a ratioof the mass of the charm quark to the massof the strange quark. As the charm mass iswell known, the researchers can estimate thestrange quark mass to be 92.4 ± 2.5 MeV/c 2(arXiv:0910.3102v2).The result will be of particular interest toresearchers at CERN’s LHCb experiment,who, by studying mesons made of bottomquarks, are trying to recreate conditions fromshortly after the Big Bang. “This is all part ofpinning down the Stan dard Model and askinghow nature can tell the difference be -tween matter and antimatter,” says Davies.to reach its ground state is proportional to itsfrequency. As the aluminium-based “quantumdrum” used in the UCSB experimentresonates at about six billion vibrations persecond, it could reach this resonation stateat “just” 0.1 K. “A regular tuning fork, forexample, would need to be cooled by an -other factor of a million to reach the samestate,” says Cleland.The team measured the quantum state ofthe resonator by connecting it electrically toa superconducting quantum bit, or “qubit”,that was used to excite a single phonon in theresonator. This excitation was then transferredmany times between the resonatorand qubit to enable the researchers to createa superposition state in the resonator wherean excitation and a lack of excitation existedsimultaneously. When the researchers meas -ured the state, via the qubit, the resonatorhad to “choose” which state it was in (Nature464 697). The experiment could enable re -searchers to study the boundaries betweenthe quantum and classical worlds.Physics World May 2010

physicsworld.comFrontiersScience/AAAS3D invisibility cloak unveiledWhile this dented cuboid may not look particularly magical, it represents a key breakthrough in one of themore mind-bending areas of physics – the pursuit of invisibility. It is the first device that can hide an objectfrom near-visible light in three dimensions – albeit a very small bump with a height of just 30 μm. Thedesign is known as a “carpet cloak” because it involves smoothing out a bump on a surface as if flatteningout a ruck in a rug. The cloak was fabricated by Tolga Ergin and colleagues at the Karlsruhe Institute ofTechnology (KIT) in Germany, together with John Pendry of Imperial College London. The team built thecloak by stacking nanofabricated silicon wafers on top of one another in a “woodpile” matrix and thenfilling in the gaps between the wafers with varying amounts of polymer. This produces a distribution ofrefractive indices within the structure that can achieve an optical transformation whereby light appears toreflect off the device as if an object were not there. To demonstrate the technique, the researchers placedtheir device on top of a reflective gold surface containing a small bump with dimensions of30 μm × 10 μm × 1 μm. This set-up produced a cloaking effect using unpolarized infrared light withwavelengths between 1.4 μm and 2.7 μm (Science 10.1126/science.1186351). Importantly, this effectheld for viewing angles of up to 60° (with 0° representing viewing in just two dimensions). Last year thissame cloaking technique was used to hide objects at micro and infrared wavelengths, but these cloakswere limited to two dimensions. Team member Martin Wegener from KIT says that it should be possiblewith existing technology to make the cloak bigger in order to hide even larger objects, but that thisapproach would be extremely time-consuming. “Faster nanofabrication tools will have to be developedthat allow for 3D structures,” he says.Antenna shrunk for the nanoworldNanotechnology in science fiction usuallyinvolves familiar objects being cleverlyshrunk to the scale of individual molecules.In a rare example of that vision becominga reality, researchers in Japan have built anano-scale version of a classic TV antennabut in this case it can transmit light.The “Yagi–Uda” antenna was invented byJapanese scientists in 1926 to overcome signaldegradation, whereby radio signals de -grade when transmitted over long distances.It was used by the British with radar duringthe Second World War and went on to be -come the standard antenna for transmittingand receiving television signals. Key to theclassic design is its “parasitic elements”,made from strips of electrical conductors,which boost radio transmissions by produ -cing secondary signals in the same directionwhen a current is induced in the presence ofPhysics World May 2010the original signal. The same principle worksin reverse, so the antenna can also boost a signalwhen receiving information.Yutaka Kadoya and colleagues at Hiro -shima University have now adapted theYagi– Uda design to control light at the nanoscaleby replacing the conducting strips withan array of five gold nanorods. The nanorodsare aligned in such a way that incoming lightmanages to trigger plasmons in the gold surface– collective wavelike motions of billionsof electrons – to resonate and emit secondarylight in the same direction. The re searchersdemonstrated the technique for red light witha wavelength of 662 nm (Nature Photonics10.1038/nphoton.2010.34). They now want tointegrate their design with fluorescent moleculesto create a coupled device that couldform the basis of a new sensing technique forthe medical sciences.InnovationTiny desalination devicecould help aid effortsEach year, two million people – mostly children –die from water-borne diseases such as diarrhoeaand cholera, according to the United Nations.Particularly vulnerable are those affected bynatural disasters, when gaining access to cleanwater can be a problem. However, a new techniquethat produces drinking water from seawater usingjust small amounts of energy could help to addressthis dire situation.The technique, developed by researchers at theMassachusetts Institute of Technology (MIT) in theUS and Pohang University of Science andTechnology in Korea, manages to desalinate waterusing a simple electronic system. The processstarts by passing water along a tiny, 500 μm widechannel on a polymer chip. When the waterreaches a junction, it splits off into two separatetubes. By applying an electric potential along oneof these tubes, salt ions are dragged towards thischannel in the form of brine, while desalinatedwater flows down the second channel under theforce of gravity. The researchers have successfullyused the technique, which is dubbed ionconcentration polarization (ICP), to convertseawater, with a salinity of 30 000 mg l –1 , intofresh water with a salinity of less than 600 mg l –1 ,which meets the international standards for waterpurity (Nature Nanotech. 5 297).In terms of energy consumption, ICP comparesfavourably with established methods ofdesalination, requiring less than 3.5 Wh l –1 .Reverse osmosis, for example, which works byforcing seawater through a membrane at highpressures to capture the salt, requires 10–15 Wh l –1 . And electrodialysis, which works bytransporting salt ions from one solution to anotherby means of ion-exchange membranes, requires5 Wh l –1 . Another advantage of ICP is that it canremove other potentially harmful larger molecules– such as cells, viruses and bacteria – without thefilter becoming heavily clogged, a problem thataffects both reverse osmosis and electrodialysis.The next challenge is to scale up the device intoa viable technology. As one chip produces just10 μl per minute, the researchers estimate thatthey will need 10 000 combined units to produce auseful amount of water in a realistic time. A devicethis size would still be portable at just 30 × 20 cm.Sung Jae Kim, one of the researchers at MIT,told Physics World that his team hope to haveproduced a 100-unit device within two years.One outstanding challenge is to ensure that alldangerous hydrocarbons and heavy metals arealso removed from the seawater, which is notguaranteed with the current device.5

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physicsworld.comNews & AnalysisLHC ramps up its search for the HiggsThe physics programme at CERN’sLarge Hadron Collider (LHC) is nowunder way and the Geneva lab says itis making good progress with increasingthe number of proton–proton col -lisions. The first collisions at 7 TeV,marking the start of the LHC’s phys -ics programme, occurred on 30 Marchand all four of the LHC’s experimentshave been collecting data since then.“A lot of people have waited a longtime for this moment, but their pa -tience and dedication are starting topay dividends,” said CERN directorgeneralRolf-Dieter Heuer.Heuer’s delight at the LHC finallycolliding protons 18 months after itsstart-up, was shared by Fabiola Gia -notti, spokesperson for the ATLASex periment. “The prevailing sentimentis emotion,” she said shortlyafter the first collisions were an -nounced. “Behind these instrumentsare people with their feelings, withtheir frustrations, with their ambitions– it is the end of 20 years’ hard workwithin the scientific community.”Researchers at the lab are so farpleased with the quality of the collisiondata they have received. “By autumn,it is going to get quite interesting here– we will be frantically looking at thedata,” says Albert de Roeck, deputyHopes of reaching a milestone in fusionresearch by the end of 2010 have dimmedfollowing a US government report thatplays down the chances of an earlybreakthrough and sharply criticizesmanagement of the $4bn NationalIgnition Facility (NIF). In the report,officials from the GovernmentAccountability Office (GAO) state thatignition – fusion’s “break-even” point – is“unlikely” to occur at the laser-fusion labthis year and that “significant scientificand technical challenges” could delay oreven prevent the facility from achievingignition by 2012.NIF’s plan for ignition relies on beingable to focus up to 1.8 MJ energy from192 laser beams onto a 2 mm-diameterberyllium sphere filled with deuteriumand tritium fuel. Radiation pressure fromspokesperson for the Compact MuonSolenoid (CMS) ex periment. “We willhave our first pop at the Higgs at theend of the year – we will certainly ex -clude mass regions but discovery isgoing to be more difficult.”The missing piece in the StandardModel of particle physics, the Higgsboson could explain how particlesacquire their mass. Precision measurementsof known Standard Modelparticles mean that the mass of theHiggs is unlikely to be more than186 GeV, while direct searches madeat CERN’s Large Electron–Positroncollider (LEP) – the forerunner to theLHC – have ruled out a Higgs that isFusionBreakthrough at NIF ‘unlikely’ in 2010Physics World May 2010[We] neverclaimed itwould achievefusion ignitionin 2010Watchful eyesStaff in CERN’scontrol room await7 TeV collisions.the beams will then cause the sphere toimplode, fusing the deuterium andtritium nuclei and setting off a sustainedburn that produces excess energy(see pp28– 33).Although a NIF spokesperson toldPhysics World that the lab “never claimedit would achieve fusion ignition in 2010”,expectations of an early breakthroughhad been raised in January, after NIFresearchers published results showingthat they could compress plastic testspheres smoothly at radiationtemperatures of up to 3.3 mK. Testsperformed shortly after the facilityopened in March 2009 had alreadydemonstrated that laser systems couldoperate at the high energies required.But while the GAO acknowledges that“substantial progress” has been made, itCERNlighter than 114 GeV.Some researchers, however, be lievethat it could take much longer toprove decisively whether the Higgsdoes exist. “From previous findingsat the Tevatron [at Fermilab in theUS] and theoretical studies, it seemsmost prob able that the Higgs mass isa tick above 115 GeV,” says HanspeterBeck, a researcher at the ATLAS ex -peri ment. “And, if it is there, it will beultra difficult [to find] and will take upto six years to prove or disprove if itex ists,” he adds.Meanwhile, Niko Neufeld, a staffscientist at the LHCb experiment,which will study the difference be -tween matter and antimatter with un -precedented accuracy, is optimisticthat it can start producing “seriousphysics” within a few months. “To -wards the end of this year we shouldbe in full swing and hopefully have thefirst drafts of pa pers for the winterconferences of next year,” he says.CERN plans to run the LHC continuouslyfor 18 to 24 months, with ashort technical stop at the end of 2010.The LHC will then shut down in 2012to prepare it to go to maximum-energy14 TeV collisions, probably in 2013.James DaceyGenevalashes out at the management of theproject. In particular, the report finds thata “weak oversight” by the NationalNuclear Security Administration (NNSA)has allowed NIF’s operator, the LawrenceLivermore National Laboratory, to delayconstruction of safety systems requiredfor ignition experiments. These includedconcrete doors needed to containradiation from neutrons produced innear-ignition reactions.The NIF spokesperson says thatresearchers will initially performdiagnostic tests using ordinary hydrogen,rather than deuterium, to keep neutronlevels low. The proportion of deuteriumwill then be slowly increased, untilconditions are met for a full ignitionexperiment using 50% deuterium and50% tritium. The spokesperson adds thatthe “first credible attempts” at fusionwould still begin in 2010, emphasizingthat ignition is still expected within a yearor two.Margaret Harris7

News & Analysisphysicsworld.comInnovationSpin-out puts new spin on wind-energy technologyThe future of wind energy could in -volve huge blades spanning half akilometre that generate compressedair – which is then piped into giant,underwater balloons. That is thedream of Seamus Garvey, a mechan -ical engineer at the University of Not -tingham in the UK, who envisagesusing the pressurized air to inflatethe balloons, nestling about 500 mbelow the surface of the sea. Elec tri -city could then be generated, when re -quired, by releasing the air to drive aset of turbines.The advantage of Garvey’s techniqueis that several days’ worth ofenergy could be stored in the balloonswhile the wind is blowing – and thenreleased when there is no wind. Gar -vey has just formed a spin-out companycalled NIMROD Energy tocommercialize the technology, dub -bed Integrated Compressed Air Re -newable Energy Systems (ICARES),which he has been working on since2006. He has also received a 7310 000development grant from the energycompany E.ON.According to Garvey’s blueprint,the wind turbine’s blades would behollow and contain an internal piston.When the blade is pointing downwards,the piston is at the tip. As theblade slowly lifts skywards, the pistonChina has announced plans to generatean extra 100 GW of power from nuclearreactors – a 12-fold increase in nuclearcapacity. The plans, released in lateMarch by the Energy Bureau of theChinese National Development andReform Commission (NDRC), will see anadditional 75–80 GW of nuclear powercoming online by 2020, with a further25 GW of capacity still under constructionat that time. If the country completes itsplan, then nuclear power will accountfor about 5% of China’s electricity needsby 2020.Last year, nuclear power capacity inChina was 9.08 GW, accounting for only1.04% of the total power generation inthe country, according to the ChinaElectricity Council, which implementsgovernment energy policy. Original plansby the NDRC, published in October 2007,announced that China would increase itsfalls through the cylinder, compres -sing air. However, the blades must notrotate too fast or else the pistons willget pinned to the ends of the blades.Given that a blade’s rotation speed isinversely proportional to its length,Garvey’s scheme would only be practicalfor turbines bigger than about230 m in diameter, with 500 m beingthe ideal size.As for the storage balloons, Garveysays they should ideally be 20 m indiameter and lie anchored 500 mbelow the surface of the sea. He hasal ready begun to test prototype “en -ergy bags” and believes that that acommercial undersea storage systemwill be available by May next year.EnergyChina plans massive nuclear boost8Power to the peopleOne of two 1.75 GWEuropean PressurizedReactors that China isbuilding in TaishanCity, near Hong Kong.Bags of energySeamus Garvey fromthe University ofNottingham hasdesigned a way ofstoring wind energy inunderwater balloons.nuclear power capacity by 40 GW by2020 with a further 18 GW inconstruction. The revised plans almostdouble those figures.“We will be building as many as six toeight 1 GW nuclear power plants eachyear,” says Mu Zhanying, general managerof Chinese National Nuclear EngineeringGroup Company. Chinese authorities haveUniversity of NottinghamChina Guangdong Nuclear Power GroupAlthough Garvey believes that it willtake about 15 years to get the giantturbines up and running, he says hissystem could be as cheap to build as agas-turbine generator and have zerofuel costs.Compressed-air energy storage isnot a totally new idea. There are twofacilities – one in Germany and theother in the US – where surplusenergy is taken off the electrical gridand used to pump air undergroundinto disused salt mines. But Garveysays that underwater storage has twobenefits. It is not restricted to minelocations, plus the pressure in an un -dersea bag is constant, which lets turbinesgenerate electricity relativelyefficiently. An underground storagefacility, in contrast, has a fixed volume,meaning that the air pressuredrops as air is released.Garvey also thinks undersea bagscould store surplus energy from nuc -lear reactors or even natural gas.Jakob Mann, a wind-energy expert atRisø National Laboratory in Den -mark, says that the storage techniqueis “worthwhile trying” but warns thatthe undersea nature of the schemecould boost the cost. “Offshore is al -ways expensive,” he says.Hamish Johnston● See also page 14identified 30 possible sites that canaccommodate nuclear power stations.China is already building the world’slargest single nuclear power plant inTaishan City, on the southern coast of thecountry, close to Hong Kong. The 1.75 GWTaishan nuclear plant, costing $4.7bn, isthe first of two European PressurizedReactors to be built at Taishan and isexpected to come online in 2013, with thesecond following in 2014. Indeed,Sun Youqi, general manager of ChineseNational Nuclear Engineering GroupCompany, says that China is alreadybuilding more nuclear power capacitythan any other country in the world.However, some worry about China’sability to deal with nuclear-fuelreprocessing and high-level radioactivewaste once the reactors are operating.“We need to pay far more attention nowto researching techniques into fuelpost- processing”, says Li Yongjiang, theformer manager of the Qinshan NuclearPower Company.Jiao LiBeijingPhysics World May 2010

physicsworld.comNews & AnalysisSpaceObama sets out NASA’s new mission to MarsUS President Barack Obama has an -nounced a new direction for NASAthat includes plans to send astronautsto an asteroid by 2025. Speaking lastmonth at Florida’s Kennedy SpaceCenter, the launching location forUS manned spaceflights, Obama alsocalled for a new “heavy-lift” rocketdesign to take astronauts on a missionto orbit Mars by the mid-2030s thatwill “eventually” be used to transporthumans to the Martian surface.In February, the Obama admin -istration said it was cancelling theConstellation programme – first proposedby George W Bush in 2004 –to develop new “Ares” rockets thatwould allow astronauts to return tothe Moon by 2020. Critics argued thatthe decision would surrender USlead ership in space and extinguishthe country’s vision of exploration.Neil Arm strong, the first man to walkon the Moon, called the decision“devastating” and a waste of the$10bn in vestment in Con stellationand the years of re search and developmentput into the project.The new plan involves retainingsome of Constellation’s technology,and NASA will now start to adaptits Orion crew capsule, which wouldhave hitched a ride on Ares to theA satellite that will probe how muchthe Antarctic and Greenland icesheets are contributing to global sealevelrises was successfully launchedfrom the Baikonur Cosmodrome inKazakhstan last month. The 7135mCryoSat-2 satellite, built by the Eu ro -pean Space Agency (ESA), will alsomeasure tiny variations in the thicknessof ice floating in the polar oceans.Weighing 700 kg, CryoSat-2 is noworbiting the Earth around its poles720 km above sea level.CryoSat-2’s main instrument is theSynthetic Aperture InterferometricRadar Altimeter (SIRAL), which isdesigned to send a burst of microwavepulses towards the Earth every 50 µs.The returning echoes can then beused to measure the distance betweenthe satellite and the sea ice, fromwhich a 3D map of the thickness offloating sea ice lying above sea levelcan be built to an accuracy of a fewInternational Space Station (ISS), asa kind of “space lifeboat” to re ducere liance on foreign vehicles for rescuemissions to the ISS.Obama also announced that NASAwill now invest more than $3bn in re -search on its heavy-lift rocket, with adesign expected to be complete “nolater” than 2015. The rocket, whichshould be complete a few years later,could be used for a trip to a near-Earth asteroid and then in a separatemission to Mars.Obama noted that he expects to still“be around” by the time US astronautsland on the red planet. “We willEurope’s ice mission successfully blasts offPhysics World May 2010Second time luckyThe European SpaceAgency’s CryoSat-2satellite will monitorice thicknesses.One giant leapNASA plans to sendastronauts on amission to orbit Marsby the mid-2030s,with a landing sometime after.centimetres. Researchers can thenuse this information to estimate thetotal mass and thickness of ice flow,the bulk of which (some 90%) liesunder the water.Set to remain in orbit for the nextthree years, CryoSat-2 will use thesame technique to measure changes tothe thicknesses of huge land-ice sheets,NASAP Carril/ESAac tually reach space faster and moreoften under this new plan, in ways thatwill help us improve our technologicalcapacity and lower our costs,” hesaid. “Nobody is more committed tohuman exploration of space than I am.But we’ve got to do it in a smart way.”The new plans also include modernizingthe Kennedy Space Center,as well as upgrading its launch capabilities.That process should createmore than 2500 extra jobs in the re -gion, compensating in part for joblosses that will occur due to the plan -ned end of the Space Shuttle programmethis year. Obama called aswell for NASA and other governmentagencies to develop a plan by 15 Au -gust for economic growth and job creationin the region.In his speech, Obama also ex -plained where an additional $6bnover the next five years for NASA willbe spent. First announced in his 2011budget request to Congress, this newmoney will go on increasing Earthbasedobservations, extending the lifeof the ISS by more than five years to2020, as well as working with privatecompanies to make getting to spaceeasier and more affordable.Peter GwynneBoston, MAsuch as those in the Antarctic andGreenland. CryoSat-2 is the satellite’ssecond incarnation after CryoSat-1was destroyed by a launch failure fiveyears ago. In 2006 ESA decided torebuild the satellite and launch it in2009, but delays led to the take-offbeing postponed until last month.“We are very much looking forwardto delivering the data the scientificcommunity so badly needs to build atrue picture of what is happening inthe fragile polar regions,” says physicistRichard Francis, project managerof CryoSat-2. CryoSat-2 is the third ofseven Earth-monitoring satellites thatform the ESA’s Earth Explorer programme.The first – the Gravity Fieldand Steady-state Ocean CirculationExplorer (GOCE) – was launched inMarch 2009, while the Soil Moistureand Ocean Salinity (SMOS) spacecrafttook off last November.Michael Banks9

News & Analysisphysicsworld.comSidebandsClimate inquiry clears researchers“We saw no evidence of any deliberatescientific malpractice in any of the work ofthe Climatic Research Unit and had it beenthere we believe that it is likely that wewould have detected it.” That is the mainconclusion of an independent panel ofscientists, nominated by the UK’sRoyal Society, to scrutinize the scientificmethodology of researchers at the ClimateResearch Unit (CRU) at the University ofEast Anglia. The seven-member panel wasset up by the university and chaired byLord Oxburgh – a geologist and formeroil-company executive. The report, whichlooked at 11 “representative publications”from CRU members over the past 24 years,was commissioned after private CRUe-mails were hacked last year and madepublic. Critics alleged that the e-mailsshowed that the scientists incorrectlyinterpreted data to support man-madeclimate change and flouted freedom-ofinformationrequests to make data andcomputer code available.Egypt tops African physics outputEgypt, Nigeria and South Africa dominatescientific output in Africa, according to anew study from Thomson Reuters. It foundthat researchers in Egypt were the mostprolific in the north of the continent,accounting for 30 000 papers between1999 and 2008 – three times more thanfrom scientists in Tunisia. Nigeria was thedominant nation in central Africa,generating 10 000 papers in the sameperiod, while scientists in South Africa ledthe way in the south of the continent,publishing 47 000 papers in the decade to2008. Egypt is Africa’s top nation forphysics – producing 1880 papers between2004 and 2008. South Africa was secondwith 1194 papers and Algeria third with933 published articles.Diamond wins £110m upgradeThe Diamond synchrotron light source inthe UK has received £110m of funding thatwill allow it to complete 10 morebeamlines. The planned upgrade, whichshould be completed by 2017, will bringthe total number of beamlines at thefacility to 32. The bulk of the money(£97.4m) comes from the Large FacilitiesCapital Fund (LFCF), which supportsinvestments made by Research CouncilsUK – the umbrella organization for theseven UK funding councils. The remaining£13.8m comes from the Wellcome Trust –a UK-based biomedical charity. Diamondcurrently has 17 operational beamlines,which in two years’ time will be extendedto 22.10Space scienceUK launches space agency to manage all contractsA new body that will be responsiblefor the UK’s space policy and bringall key budgets for space under asingle management was establishedlast month. The UK Space Agency(UKSA) will manage about £250m incontracts each year, including theUK’s contribution to major Europeanprojects such as the 73.4bn Galileoglobal positioning system and theGlobal Mon itoring for Environmentand Security initiative. Both projectsare currently supported by the UK’sdepartment for transport, and the de -partment for environment, food andrural affairs, respectively.The UKSA, which will have itshead quarters in Swindon, will be ledby David Williams, director generalof the British National Space Centre,until a permanent chief executive isappointed within the next six months.“The action we are taking shows thatwe’re really serious about space,”said science minister Lord Draysonat the agency’s launch last month. Heclaimed that the agency will helpthe UK’s space industry to grow from£6.5bn to £40bn a year and createAn Iranian physicist who disappeared lastJune during a pilgrimage to Mecca inSaudi Arabia has apparently defected tothe US, where he is working for theCentral Intelligence Agency (CIA).Shahram Amiri, who did research innuclear physics at Malek AshtarUniversity of Technology in Tehran, isthought to be co-operating with the CIA toconfirm their intelligence assessmentsabout Iran’s nuclear-weaponsprogramme. The CIA has so far kept quieton the issue and it remains unclearwhether Amiri had any connections withIran’s nuclear programme.According to various reports, Amiri wasinvolved in producing radioactive isotopesfor medical applications at Malek AshtarUniversity of Technology. The universitylies across the street from FEDAT – aninstitution run by the country’s Ministry ofDefence that carries out research anddevelopment on nuclear weapons.According to the Washington-basedorganization Iran Watch, in 2005 officialsin Germany linked the university to workon proliferation-sensitive nuclearactivities and the development of rocketsOn the upThe UK Space Agencywill manage about£250m in contractseach year.100 000 jobs within the sector overthe next 20 years.The UK currently spends about£300m per year on civil space re search,a large fraction of which – some£240m in 2009 – goes on the country’smembership of the Euro pean SpaceAgency (ESA). The rest of the cash isspent on its membership of the Eu ro -pean Organisation for the Exploi -tation of Meteorological Satel lites,which launches and maintains Earthobservationsatellites and is currentlyfunded by the UK’s Met Office.At the UKSA launch, Drayson andbusiness secretary Lord Mandelsonalso announced a £40m InternationalSpace Innovation Centre (ISIC) to bebased at Harwell in Oxfordshire nextto the European Space Agency’s technicalfacility, which opened last July.Designed to bring together industryand academia, ISIC will seek to ex -ploit data from Earth-observationsatellites, use space data to understandclimate change, and advise onthe “security and resilience of spacesystems and services”.Michael BanksMiddle EastIranian physicist ‘defects’ to the USOnce you haveacquired theknowledge ofuraniumenrichment,it is almostimpossible toremove itfor nuclear weapons.Reza Mansouri, a physicist at Iran’sSharif University of Technology, toldPhysics World that he had never heard ofAmiri’s name before it came to light in themedia. “So you can imagine how he stoodin the physics community in Iran,” hesays. According to Steven Miller, aspecialist on Iran at Harvard University’sKennedy School of Government, itappears most likely that Amiridisappeared voluntarily.Amiri is not the first individual withsuspected connections to Iran’s nuclearprogramme to disappear and reappear inthe West. Possibly the best known isAli Reza Ashghari, a former deputydefence minister, who disappeared froma hotel in Istanbul three years ago andreportedly provided intelligence to theCIA. But Amiri’s loss is unlikely to affectthe Iranian nuclear programme. “Onceyou have acquired the knowledge ofuranium enrichment,” says Miller’scolleague Jason Blackstock, “it is almostimpossible to remove it.”Peter GwynneBoston, MAPhysics World May 2010

physicsworld.comNews & AnalysisPolicyUS changes course on nuclear-weapons strategyUS President Barack Obama has signalleda new approach to nuclearweaponspolicy that limits their useagainst other states and documentshow the country will ensure the viab -ility of existing stockpiles. The Nuc -lear Posture Review (NPR), whichsets out the US’s nuclear strategyover a 10-year period, also calls for ahighly skilled workforce to ensure“the long-term safety, security andeffectiveness of the nuclear arsenaland to support the full range of nuc -lear-security work”.The last NPR was conducted in2001 during the George W Bush ad -ministration, which kept its findingsclassified. The latest review, releasedlast month and made fully public, concludesthat the US will not use nuclearweapons against non-nuclear statesthat are “in compliance” with theNuc lear Non-proliferation Treaty,even if they attack the US with biologicalor chemical weapons. How -ever, the review makes it clear thatNorth Korea and Iran do not fall intothat category.Carried out by the US Departmentof Defense and the Department ofEnergy, the review notes the need forhighly trained scientists and engin -eers to “sustain a safe, secure andeffective US nuclear stockpile as longas nuclear weapons exist”. It alsosays that existing nuclear weapons’lifetimes could be increased, rulingout the need for manufacturing new“reliable” replacement warheads.This had been recommended late lastyear by the JASON advisory group –a collection of independent scientistswho advise the US government onscience issues.Some disagree with Obama’s decis -ion not to update the US’s nuclearweapons. “I think the administrationSigning upUS President BarackObama and RussianPresident DmitryMedvedev havesigned a newagreement onnuclear weapons.Chuck Kennedyhas made a mistake by not supportingthe [production of] reliable replacementwarheads,” says Jay Davis,found ing director of the DefenseThreat Reduction Agency and a formerLawrence Livermore NationalLaboratory scientist who is now presi -dent of the Hertz Foundation.Immediately following the review,Obama and Russian President DmitryMedvedev signed up to the START-IITreaty, which will dramatically reducethe number of deployed nuclearweapons that each country has from1762 to 1550 for the US and 1741 to1550 for Russia. Although the Senatemust ratify the treaty by a two-thirdsmajority before it can come into force,it was welcomed by JASON memberSidney Drell, a senior fellow at Stan -ford Uni versity’s Hoover Insti tutionand former deputy director of theSLAC National Accelerator La bor at -ory. “Re ducing the reliance on nuclearweapons and reaffirming the commitmentto go to zero is a strong and goodbasis,” he says. “And the commitmentto continued support for a science andtechnology base is important.”Peter GwynneBoston, MAUK parties spell out science policies ahead of 6 May general electionConservativesAdam AfriyieShadow minister forinnovation, universitiesand skillsBackground: After a BSc inagricultural economics fromImperial College London, in1993 Afriyie became founding director of ConnectSupport Services – an IT services company. Afriyiewas elected as MP for Windsor in 2005. After servingin a range of committees on civil aviation and onscience and technology, he was made Conservativeparliamentary leader for technology, media andtelecoms in 2006 and then shadow minister forinnovation, universities and skills in 2007.Pearls of wisdom: “Our science base is a valuablenational asset. Economically, politically andsocially, it underpins the prosperity and wellbeingof our nation.”What the manifesto says: “Initiating a multi-yearscience and research budget to provide a stableinvestment climate for research councils.”Manifesto wordcounts: science/scientists (8);innovation (8); research (9); universities (14);physics (0)LabourPaul DraysonMinister for science andinnovationBackground: Draysoncompleted a BSc inproduction engineering atAston University in 1982,gaining a PhD in robotics in 1985. After becomingmanaging director of Lambourn Food Company in1986, he co-founded the Oxford-based vaccinecompany PowderJect Pharmaceuticals in 1993,where he was chairman and chief executive until2003. In October 2008 he was appointed as theminister of state for science and innovation, takingup a seat in the cabinet. In June 2009 he took onadditional responsibilities as defence minister.Pearls of wisdom: “Science isn’t peripheral to thedecision facing the country. It is central: to growth,to prosperity and wellbeing.”What the manifesto says: “We are committedto a ring-fenced science budget in the nextspending review.”Manifesto wordcounts: science/scientists (6);innovation (11); research (7); universities (17);physics (0)Liberal DemocratsEvan HarrisLiberal Democratsspokesperson for scienceBackground: Evan Harris is aqualified doctor, havingcompleted his education atthe Oxford Medical School.After working as a junior doctor at theRoyal Liverpool University Hospital and theJohn Radcliffe Hospital in Oxford, Harris became anMP for Oxford West and Abingdon in 1997. In 2001he became shadow secretary of state for health,and since 2005 he has been the Liberal Democratspokesperson for science.Pearls of wisdom: “We recognize that science,technology and engineering have to be key driversof our economy as we move out of recession.”What the manifesto says: “In the current economicclimate it is not possible to commit to growth inspending, but the Liberal Democrats recognize theimportance of science investment to the recoveryand to the reshaping of the economy.”Manifesto wordcounts: science/scientists (12);innovation (5); research (9); universities (8);physics (0)Physics World May 201011

News & Analysisphysicsworld.comBreaking the vacuumEurope is planning to build the world’s most powerful laser that willliterally rip empty space apart. Michael Banks lifts the lid on theExtreme Light InfrastructureThis year is one of celebration for Gér -ard Mourou – and not just because2010 marks the 50th anniversary of theinvention of the laser. It is also 25 yearssince the 65-year-old French physicistpublished details of one of his mostcoveted contributions to laser science.Going by the rather ungainly name ofchirped-pulse amplification (CPA),the technique has enabled physiciststo create lasers that are orders of magnitudesmore powerful than wereachievable without it (see box).CPA now lies at the heart of mosthigh-powered laser facilities in theworld. It was used in the now-decommissionedNova PW system at theLawrence Livermore National La bor -atory in the US, which generatedrecord-breaking 1.3 PW (1.3 × 10 15 )pulses, and in the 1 PW Vulcan laserat the UK’s Rutherford Appleton La -boratory in the UK, which is in themidst of being upgraded to go beyondthe 10 PW level.But now Mourou is designing alaser facility that will be so powerfulthat it can rip apart empty space itself.Mourou’s parting shot to the lasercommunity, the Extreme Light Infra -structure (ELI) will create very shortpulses of light barely 1 femtosecond(10 –15 s) long with energies of severalkilojoules corresponding to petawattsof power. While other lasers such asVulcan can provide a high-poweredpulse every 20 minutes, ELI will beable to deliver one every few minutes.Four for the futureThe Extreme LightInfrastructure willconsist of fourfacilities, includingthis one in theCzech Republic thatwill use short pulsesof light to testacceleratingelectrons with lasers.Although ELI will be used for nuc -lear physics, attosecond physics andstudies of laser-based particle acceleration,perhaps its most exciting possibilityis to test the properties of thevacuum, or empty space, itself. “Thisis not just a laser that is about breakingthe next re cord,” says Mou rou,who is ELI’s project coordinator anddirector of the Institut de la Lu mièreExtrême at the Ecole Na tion ale Su -périeure de Tech niques Avancées inFrance. “There is a fundamental reasonbe hind building it.”Mourou first proposed ELI fiveyears ago and he has been the drivingforce behind the project ever since. In2006 it was chosen as one of 35 projectson a “wish list” of scientific facilitiesdrawn up by the European StrategyForum on Research Infra structuresthat researchers in Europe want to seeHamiltons Architectsbuilt within the next decade.The new laser facility quickly garneredsupport with laser scientists inEurope, including Wolfgang Sander,director of the Max Born Institute fornonlinear optics and short-pulsespectroscopy in Berlin and the president-electof the German PhysicalSociety. “ELI offers a factor of 100more in achievable power than anywhereelse in the world,” he says. “Alot of new physics could be done withit – it is revolutionary.”A competition to build ELI wasbegun in 2007. Five countries – theCzech Republic, France, Hungary,Romania and the UK – initially bid tohost the project. But after the UK andFrance pulled out of the running, inOctober 2009 the ELI steering committeedecided to not build one singlefacility, but four – one in Romania onnuclear physics, another in Hungaryon attosecond physics, a third onlaser-based particle-beam productionin the Czech Republic and a fourth inultrahigh-powered lasers. The latter’slocation is still up for grabs.The 7250m needed to build each ofthe first three of these facilities will bemet by the host nation and constructionis due to start at the end of theyear. Once up and running in 2015, anumber of European member statesbe longing to the European ResearchInfrastructure Consortium are expectedto pay for labs’ operational costs.Surfing electronsThe Czech facility, which will be builtin Prague, will seek to generate forthe first time pulses with a few peta -watts in power at a frequency of about100 Hz. These femtosecond laser pul -ses will be fired into a gas to create anelectron–proton plasma that could beused to make a very compact particleShining light in the femtosecond regimeAll four sites belonging to the Extreme LightInfrastructure project have one aspect in common:a way of generating very short pulses of light atvery high energies. At their heart, the four facilitieswill use the chirped-pulse amplification (CPA)technique invented 25 years ago by GérardMourou, now director of the Institut de la LumièreExtrême at the Ecole Nationale Supérieure deTechniques Avancées in France.To generate the high-energy beams, a standardoff-the-shelf table-top laser source will be used togenerate pulses that are a femtosecond in length.These pulses, however, only have a small amountof energy – about a nanojoule. To get a highpoweredpetawatt beam, the energy needs to beincreased by a factor of about 10 12 . However, asthe energy of a short-pulse laser beam is12amplified, the refractive index of the medium it ispassing through starts to change; and once thepower of the beam goes beyond a few gigawatts, itstarts to produce nonlinear effects in the medium.This can lead to so-called self-focusing, where theintensity of the beam increases rapidly damagingthe optics in the process.To keep the intensity of laser pulses below thethreshold of nonlinear effects, laser systems hadto be very large and expensive, and the peak powerof laser pulses was still limited to a few terawattsfor very large multibeam facilities. In 1985Mourou, then at Rochester University, US, andhis colleague Donna Strickland, developedCPA to get around the nonlinear effects (OpticsCommunications 56 219). It works by taking theshort pulse and passing it through a pair ofgratings that stretch the pulse in time by a factor ofa 100 000. The gratings are arranged so that thelow- frequency component of the laser pulse travelsa shorter path than the high-frequency componentdoes, so the high-frequency component lagsbehind the low-frequency component and thepulse spreads out in time.As the pulse is longer, its power is lower and itsenergy can then easily be increased by passing thepulse through a amplifier such as a titanium–sapphire crystal. The amplified pulse is thenpassed through a second pair of gratings thatreverse the dispersion – forcing the high-frequencycomponent of the laser pulse to travel a shorterpath and the low-frequency component to travel alonger path, so the pulse then “recombines” into ashort femtosecond pulse.Physics World May 2010

physicsworld.comNews & Analysisaccelerator. As the laser pro pagatesthrough the plasma, the electrons areexpelled around the laser pulse – justas a boat displaces water around it asit moves forward. As the electronsthen rush back in behind the laserpulse, they set up a trailing wave-likestructure known as a “wakefield” –like a water wave travelling behindthe boat. Other plasma electronstrap ped by these waves “surf” onthem behind the laser pulse pickingup energy and accelerating.This technique allows laser lightto accelerate electrons over a muchsmaller distance than conventionalparticle accelerators, which can betens of kilometres long. “Typically, wethink we can achieve electron energiesof about 10–20 GeV,” says Mou -rou. “So instead of building a 1 kmlin ear accelerator, we can instead usesomething that is only 1 m long.”Mourou says that the Prague ELIcentre, which could also accelerateprotons for use in hadron therapy,will complement, rather than replace,other facilities that generate shortpulses of X-rays, such as the LinacCoherent Light Source (LCLS) at theSLAC National Accelerator Labor at -ory. But while LCLS, which is an X-rayfree-electron laser, can only producemonochromic radiation with pulsedurations of the order of 100 fs, ELIcould produce polychromatic ra di -ation of the order of a femtosecond orless, making it possible to take imagesof chemical reactions in real time.“ELI is pushing the boundaries interms of testing this technology toprovide a range of applications,” saysJohn Collier, head of the high-powerlasersdivision at the Central LaserFacility at the Ruther ford lab.Ripping atomsELI’s nuclear-physics facility in Ro -mania is set to be built in Ma gu rele,20 km south of Bucharest. The facilitywill produce 10 PW beams that areshone directly onto a nucleus to studyhow the pulse affects nuclear energylevels. Researchers expect that thelaser pulse should be able to depositabout 1–10 keV on the nuc leus –enough to modify energy levels andforcing it to release a gamma ray. De -tecting this radiation would be proofthat researchers have affected thenucleus directly with laser light, thusallowing them to study nuclear trans -itions in more detail.As for the Hungarian “attosecond”facility, it will use a 5 fs pulse with alaser beam of a few joules to generatepowers of the order of a petawatt. Thefacility, to be built in Szeged, 100 kmPhysics World May 2010south of Budapest, will generate pulsesevery 1 ms that will be used to takesnap-shots on the attosecond scale(10 –18 s) of electron dynamics in atoms,plasmas and solids. It will do this byshooting a femtosecond pulse of lightat a dense plasma target. In a processknown as “relativistic harmonic generation”,the ionized plasma then givesoff so-called phase-locked radiation inthe ultraviolet and soft X-ray regimeat multiples of the frequency of theoriginal femtosecond pulse. Research -ers at ELI will then select the pulsesthat are generated in the atto secondregime with a filter and send them toexperimental stations to study materialson the atomic scale.Boiling the vacuumThe host for what is dubbed the“heart” of ELI – the “ultrahigh peakpower” facility – will not be knownuntil 2012, after some initial testingof technology for the three main fa -cilities is carried out. With an ex -pected completion date of 2018, thefacility will attempt to generate a100– 200 PW beam and use mirrors tofocus it onto an area of 1 µm 2 in thehope of ripping open the fabric of thevacuum to produce particle and anti -particle pairs. “The vacuum is notsomething empty, but is full of activityof particles being created and de -stroyed,” says Mourou. “It defines allthe constants of physics.”Quantum field theory states these“virtual particles” continually pop inand out of existence. It is predictedthat paired virtual particles could be -come real as they are torn apart bythe pulse’s extremely strong electromagneticfields. How ever, this happenstoo quickly to leave a trace andrequires light with an in tensity ofabout 10 29 Wcm –2 . Known as the“Schwinger limit”, it is seven orders ofmagnitude larger than any currentlaser can achieve.In its current design, ELI’s highintensityfacility will only be able toreach 10 25 Wcm 2 ; however, MannuelParticle test-bedThe LASERIX laserat the UniversitéParis-Sud II has beentesting whether laserscan produce X-rays,as the Czech ELIfacility hopes to do.ELI will createnew scientificcommunitiesand it willbe a magnetfor hi-techcompaniesCNRS Photothèque/Alexis CheziereHege lich, project leader of shortpulseexperiments and lasers at theLos Alamos National Laboratory inNew Mexico, says there are some newtheories being proposed that couldbring the Schwinger limit within ELI’sreach. “The vacuum has energy levelsand it would be great if we couldsomehow manage to modify them,”says Hegelich. Mourou also say theSchwinger limit could be matched bycolliding electron beams created bytwo lasers.One of the technical challenges ofthe ultrahigh-peak-power facility willbe producing the vacuum itself. “Evenultrahigh-vacuum environments producedby highly efficient pumps stillhave a few atoms floating around,”says Hegelich. One method would beto first shoot a laser pulse into thehigh-vacuum environment that wouldexpel all the particles and then quicklyfollow that up with a second highpoweredpulse. “Technically, there isnothing that can’t be overcome withthe ultrahigh-peak-power facility,”says Hegelich. “It is more an engin -eering challenge that a physics one.”One phenomenon that ELI shouldbe able to detect, which is predictedto happen at about 10 23 Wcm –2 , is thevacuum becoming polarized and ex -hibiting optical phenomenon suchas birefringence. Some theorists arealready proposing experiments for theultrahigh-peak-power facility such asa “matterless” double-slit experimentwhere the photons generated fromelectron and positron pairs annihil -ating form a double-slit diffractionpattern (Nature Physics 4 92).As well as being a revolutionaryphys ics project that will test fundamentaltheories and show how laserscould become the next particle acceleratoror collider, ELI is also tippingthe scales of Europe’s portfolio ofmajor infrastructures slightly moreeastwards. The presence of threemajor facilities in the Czech Repub -lic, Hungary and Romania will allowthese nations to attract researchersfrom abroad, as well as inspiring fu -ture generations of researchers.“ELI will create new scientific communitiesand it will be a magnet forhi-tech companies,” says Sander, whonotes that for every euro spent on alarge infrastructure, 74 is given backto the economy. Yet for most physicists,it is ELI’s ultrahigh-power facility,which will provide laser power farbeyond any existing today, that is themost exciting and eagerly awaited.“Within the next decade,” says Mou -rou, “we will be en tering a new paradigmin physics.”13

physicsworld.comFeedbackLetters to the Editor can be sent to Physics World,Dirac House, Temple Back, Bristol BS1 6BE, UK,or to pwld@iop.org. Please include your address anda telephone number. Letters should be no more than500 words and may be edited. Comments on articlesfrom physicsworld.com can be posted on the website;an edited selection appears hereEensey, weensey unitsYou reported last month (April p3) on theefforts of Austin Sendek, a physics studentfrom the University of California, Davis,to establish the “hella” as an officialInternational System of Units (SI) prefixfor 10 27 . You also asked for suggestions onunit prefixes that go down to 10 –27 – butsurely this is not difficult. I have longdeclared the “tini” (pronounced with an“ee” sound) to denote this quantity. Thisdesignation has the additional value ofsuggesting the subsequent two prefixes aswell: the “insi” (pronounced “eensey”) for10 –30 , to be followed closely by the “winsi”(pronounced “weensey”).I have tried to think of prefixes thatwould come in on the high end beyond“hella” but unfortunately I could think ofnothing that could not be interpreted as arude word. Maybe I should not havelimited myself to the English language.B Todd HuffmanUniversity of Oxford, UKt.huffman1@ox.ac.ukWe already have the prefix “zepto” for10 –21 , but this is clearly a mistake for“zeppo”. Could we not have groucho,chico and harpo as prefixes for 10 –27 , 10 –30and 10 –33 ?Keith DoyleWalton on Thames, Surrey, UKkeith.doyle@lloyd-doyle.comThere is no need for a new “hella” prefix, asan extended set of SI prefixes has alreadybeen suggested by Victor Mayes. Writing in1994 in the Quarterly Journal of the RoyalAstronomical Society (35 569) Mayes’suggestion for 10 27 was “nava”, from theSanskrit for nine (10 27 = 1000 9 ). He alsoComments from physicsworld.comUsually, the “most commented” articles onphysicsworld.com are those that concerncontroversial science policies, rather thanscience itself. Now and then, though, a scientificstory – in this case a proposed method forstoring wind energy in giant undersea bags –captures readers’ imaginations (“Spin-out putsnew spin on wind energy” 30 March; see alsop8). The idea would see pistons inside the bladesof giant wind turbines used to pump compressedair into storage balloons; on calm days, thestored air could be released to drive a setof turbines, thus ensuring a continuous supplyof electricity. According to inventorSeamus Garvey, a similar scheme could helpstore surplus energy from nuclear reactors. Aninteresting notion, certainly – but is there acatch somewhere?The proposal to use a bag system for storing“surplus energy from nuclear reactors” soundsfunny. It’s designed to store energy from unreliablesources, so I’d stick to that – it’s wind generatorsthat are causing mayhem on our energy grid, notnuclear plants.kasuha, Czech RepublicI agree that you should confine this system to wind,but I disagree that wind is causing havoc on thegrid. We also need to look at the environmentalimpacts, which will be significant if we startinstalling thousands of floating airbags at thebottom of the ocean. But then again, nothing isworse than coal and gas.gunslingor, USYou probably haven’t had enough blackoutscaused by wind turbines overloading the grid yet.Environmental or not (and I think these bags are farfrom environmentally friendly – they are going todamage quite large areas of sea bed), windturbines are causing many problems anddesperately need reliable means of energy storage.kasuhasuggested “sansa” for 10 30 (san-shi beingChinese for “thirty”); “besa” for 10 33 (besarmeans “great” in Malay-Indonesian) andso on up to “ultra” (Latin for “beyond,extreme”) for 10 48 . In a similar vein, Mayes’system assigned “tiso” (Arabic tis’a or“nine”) to 10 –27 ; “vindo” (from Hindivindu, “a speck”) to 10 –30 and “weto”(Maori wheto, “small”) to 10 –33 .High winds knocking down power lines is what’scausing mayhem on our grid, not wind generatorsor nuclear plants. Bring on the undersea bags!dratman, USThe bag might be a problem. I propose a simplersolution to store the air underwater: an open-endedcan or concrete caisson, sealed at the top andopen at the bottom. No moving parts.AlanMWouldn’t it be a lot easier to pump water up a hill?John Duffield, UKYes, pumping water uphill would work – but youhave to have a hill, and preferably a high one.I think an air-pump system would be moremaintenance-free than a pumping system that hasto deal with the corrosive effects of salt water.NewbeakIs the weight of the piston inside the vanes the onlything supplying force to pump the air down to500 m below sea level?feet2thefireI get a pressure of about 710 psi at 500 m. Youcould have a piston with a cross-section of0.1 square inches (just under 3/16 inch radius)weighing 71 lb. If the weight of the piston were theonly drive, it would need to be prohibitively long,possibly over 65 m if it were made of steel. Soprobably the plan would include some kind ofweight behind the piston. But the rotating partswould still need to seal against approximately710 psi, which is 49 atmospheres. This seems tome to be the killer for the engineering end of it.m.a.king, CanadaRead these comments in full and add your own atphysicsworld.comUsing Mayes’ prefixes, the power of theSun can be written as 0.38 navawatt,while the mass of the galaxy is about220 catagrams (from the Spanish catorce or“fourteen”, denoting 10 42 = 1000 14 ) andthe electron rest mass is 0.91 tisogram.J Keith AtkinUniversity of Sheffield, UKchet1@blueyonder.co.ukUHV-Leakvalvewww.vseworld.comVACUUMTECHNOLOGYGA-6890 LUSTENAU (AUSTRIA),Sandstr.29Tel:+43(0)55 77 -82 6 74Fax:+43 (0)55 77 -82 6 74-7e-mail: office@vseworld.comom14Physics World May 2010

physicsworld.comThe laser at 50Physics WorldDirac House, Temple Back, Bristol BS1 6BE, UKTel: +44 (0)117 929 7481Fax: +44 (0)117 925 1942E-mail: pwld@iop.orgWeb: physicsworld.comEditor Matin DurraniAssociate Editor Dens MilneNews Editor Michael BanksReviews and Careers Editor Margaret HarrisFeatures Editor Louise MayorWeb Editor Hamish JohnstonWeb Reporter James DaceyKate Gardner, Louise Mayor and Dens MilneAdvisory Panel John Ellis CERN, Peter KnightImperial College London, Martin Rees Universityof CambridgePublisher Jo AllenMarketing and circulation Angela GageDisplay Advertisement Sales Edward JostRecruitment Advertisement Sales Chris ThomasAdvertisement Production Mark TrimnellArt Director Andrew GiaquintoDiagram Artist Alison ToveySubscription information 2010 volumeThe subscription rates for institutions are£310/7460/$585 per annum. Single issues are£25.00/736.00/$47.00. Orders to: IOP CirculationCentre, Optima Data Intelligence Ltd, 12/13 CranleighGardens Industrial Estate, Southall, Middlesex UB1 2DB,UK (tel: +44 (0)845 4561511; fax: +44 (0)870 4420055;e-mail: iop@optimabiz.co.uk). Physics World is availableon an individual basis, worldwide, through membership ofthe Institute of PhysicsCopyright © 2010 by IOP Publishing Ltd and individualcontributors. All rights reserved. IOP Publishing Ltd permitssingle photocopying of single articles for private study orresearch, irrespective of where the copying is done.Multiple copying of contents or parts thereof withoutpermission is in breach of copyright, except in the UKunder the terms of the agreement between the CVCP andthe CLA. Authorization of photocopy items for internal orpersonal use, or the internal or personal use of specificclients, is granted by IOP Publishing Ltd for libraries andother users registered with the Copyright Clearance Center(CCC) Transactional Reporting Service, provided thatthe base fee of $2.50 per copy is paid directly toCCC, 27 Congress Street, Salem, MA 01970, USABibliographic codes ISSN: 0953-8585CODEN: PHWOEWPrinted in the UK by Warners (Midlands) plc, The Maltings,West Street, Bourne, Lincolnshire PE10 9PHThe Institute of Physics76 Portland Place, London W1B 1NT, UKTel: +44 (0)20 7470 4800Fax: +44 (0)20 7470 4848E-mail: physics@iop.orgWeb: iop.orgLet there be lightThis issue of Physics World celebrates the 50th anniversary of the invention of the laserWhen Theodore Maiman eked out the first pulses of coherent light from a pinkrubycrystal on 16 May 1960, the 32-year-old engineer-turned-physicist at HughesResearch Laboratories in the US could not have imagined that the laser wouldbecome such a workhorse of physics – and so engrained in everyday life. Withinweeks, other physicists – notably those at Bell Laboratories – had reproducedMaiman’s success, with Bell Labs scientists then quickly notching up many otherlaser “firsts”, including the first gas lasers and the first continuously operatingruby lasers.Lasers have gone on to be one of the outstanding success stories in physics. Theycan cool atoms, send data, mend eyes, sharpen astronomical images and probeindividual DNA molecules; they may even detect gravitational waves and triggerfusion. Hardly surprising then that, by our reckoning, some 14 physics Nobel prizeshave been awarded for achievements directly related – or linked – to lasers. Indeed,despite their use in the military, lasers do not suffer from an image problem, beingwidely regarded as a “good thing”.This special issue of Physics World kicks off by reliving the laser’s first days and bycelebrating its impact on popular culture (think Goldfinger and laser-art shows)and everyday life (DVDs, laser pointers, bar-code scanners). We look at the technologicalimpact of lasers in fibre optics and at the quest for green-wavelengthlaser diodes that could let mobile phones project images onto any surface. Basicresearch gets a look-in, too – in terms of both ultrahigh power and ultrafast lasers.There is a timeline of laser history, while six experts predict where laser sciencewill go next. Online, don’t miss our video interviews with leading laser scientists,while the physicsworld.com blog reveals how we created our cover image and thephoto above. (As it turns out, there are some things lasers can’t do so well.)Matin Durrani, Editor of Physics WorldPhysics World May 2010The contents of this magazine, including the views expressed above, are the responsibility of the Editor.They do not represent the views or policies of the Institute of Physics, except where explicitly stated.15

The laser at 50: A cultural historyphysicsworld.comFrom ray-gunto Blu-rayThe first public reactions to lasers ranged from“Death ray!” to “Nice idea, but what good is it?”.Sidney Perkowitz reviews how lasers are nowinextricably entwined in our lives, from everydayapplications to popular cultureSidney Perkowitzis Candler Professorof Physics at EmoryUniversity, US, e-mailphysp@emory.edu.Also a science writer,his latest book –Hollywood Science:Movies, Science andthe End of the World –has just beenreissued in paperbackby ColumbiaUniversity Press16There is one particular scene in H G Wells’ 1898 taleThe War of the Worlds that, if only I had remembered it,could have helped me to avoid a bad moment in mylaser lab in 1980. In the story – published long beforelasers came along in 1960 – the Martians wreak destructionon earthlings with a ray that the protagonist calls an“invisible, inevitable sword of heat”, projected as if an“intensely heated finger were drawn… between me andthe Martians”. In all but name, Wells was describing aninfrared laser emitting an invisible straight-line beam –the same type of laser that, decades later in my lab,burned through a favourite shirt and started on my arm.Wells’ bold prediction of a destructive beam weaponpreceded many others in science fiction. From the1920s and 1930s, Buck Rogers and Flash Gordonwielded eye-catching art-deco ray-guns in their spaceadventures as shown in comics and in films. In 1951 thepowerful robot Gort projected a ray that neatly disposedof threatening weapons in the film The Day theEarth Stood Still. Such appearances established laserlikedevices in the popular mind even before they wereinvented. But by the time the evil Empire in Star WarsEpisode IV: A New Hope (1977) used its Death Starlaser to destroy an entire planet, lasers were a thing offact, not just fiction. Lasers were changing how we live,sometimes in ways so dramatic that one might ask,which is the truth and which the fiction?Like the fictional science, the real physics behindlasers has its own long history. One essential startingpoint is 1917, when Einstein, following his brilliant successeswith relativity and the theory of the photon,established the idea of stimulated emission, in which aphoton induces an excited atom to emit an identicalphoton. Almost four decades later, in the 1950s, the USphysicist Charles Townes used this phenomenon toproduce powerful microwaves from a molecular me -dium held in a cavity. He summarized the basic process– microwave amplification by stimulated emission ofradiation – in the acronym “maser”.After Townes and his colleague Arthur Schawlowproposed a similar scheme for visible light, TheodoreMaiman, of the Hughes Research Laboratories in Cali -fornia, made it work. In 1960 he amplified red lightwithin a solid ruby rod to make the first laser. Its namewas coined by Gordon Gould, a graduate studentworking at Columbia University, who took the word“maser” and replaced “microwave” with “light”, andlater re ceived patent rights for his own contributionsto laser science.Following Maiman’s demonstration of the first laserthere was much excitement and enthusiasm in the field,and the ruby laser was soon followed by the heliumneon or HeNe laser, invented at Bell Laboratories in1960. Capable of operating as a small, low-power unit,it produced a steady, bright-red emission at 633 nm.However, an even handier type was discovered twoPhysics World May 2010

physicsworld.comThe laser at 50: A cultural historyDanjaq/EON/UA/The Kobal Collectionyears later when a research group at General Electricsaw laser action from an electrical diode made of thesemiconductor gallium arsenide. That first laser diodehas since mushroomed into a versatile family of smalldevices that covers a wide range of wavelengths andpowers. The diode laser quickly became the most pre -valent type of laser, and still is to this day – accordingto a recent market survey, 733 million of them were soldin 2004.Better living through lasersAs various types of laser became available, and differentuses for them were developed, these devices en teredour lives to an extraordinary extent. While Maiman wasPhysics World May 2010dismayed that his invention was immediately called a“death ray” in a sensationalist newspaper headline,lasers powerful enough to be used as weapons wouldnot be seen for another 20 years. Indeed, the most widespreadversions are compact units typically producingmere milliwatts.A decade and a half after their invention, HeNelasers, and then diode lasers, would become the basisof bar-code scanning – the computerized registrationof the black and white pattern that identifies a productaccording to its universal product code (UPC). Theidea of automating such data for use in sales and inventoryoriginated in the 1930s, but it was not until 1974that the first in-service laser scanning of an item with aDo you expect meto talk?James Bond is heldcaptive by Goldfingerand his sci-fi redlaser that can cutthrough gold.17

The laser at 50: A cultural historyphysicsworld.comPhotolibraryTEK Image/Science Photo LibraryUPC symbol – a pack of Wrigley’s chewing gum –occurred at a supermarket checkout counter in Ohio.Now used globally in dozens of industries, bar codesare scanned billions of times daily and are claimed tosave billions of dollars a year for consumers, retailersand manufacturers alike.Lasers would also come to dominate the way in whichwe communicate. They now connect many millions ofcomputers around the world by flashing binary bits intonetworks of pure-glass optical fibre at rates of terabytesper second. Telephone companies began installingoptical-fibre infrastructure in the late 1970s and the firsttransatlantic fibre-optic cable began operating betweenthe US and Europe in 1988, with tens of thousands ofkilometres of undersea fibre-optic cabling now in ex -istence worldwide. This global web is activated by laserdiodes, which deliver light into fibres with core diam -eters of a few micrometres at wavelengths that arebarely attenuated over long distances. In this role, lasershave become integral to our interconnected world.As lasers grew in importance, their fictional versionskept pace with – and even enhanced – the reality.Only four years after the laser was invented, the filmGoldfinger (1964) featured a memorable scene thathad every man in the audience squirming: Sean Con -nery as James Bond is tied to a solid gold table alongwhich a laser beam moves, vaporizing the gold in itspath and heading inexorably toward Bond’s crotch –Lasers would come to dominate theway in which we communicate.They now connect many millions ofcomputers around the world byflashing binary bits into networksof pure-glass optical fibre at rates ofterabytes per second18though as usual, Bond emerges unscathed.That laser projected red light to add visual drama,but its ability to cut metal foretold the invisible infraredbeam of the powerful carbon-dioxide (CO 2 ) laser – thetype that once ruined my shirt. Invented in 1964, CO 2lasers emitting hundreds of watts in continuous opera -tion were introduced as industrial cutting tools in the1970s. Now, kilowatt versions are available for usessuch as “remote welding” in the automobile industry,where a laser beam directed by steerable optics canrapidly complete multiple metal spot welds. Highpowerlasers are suitable for other varied industrialtasks, and even for shelling nuts.Digital mediaAside from the helpful and practical uses of lasers,what have they done to entertain us? For one thing,lasers can precisely control light waves, allowing soundwaves to be recorded as tiny markings in digital formatand the sound to be played back with great fidelity. Inthe late 1970s, Sony and Philips began developingmusic digitally encoded on shiny plastic “compactdiscs” (CDs) 12 cm in diameter. The digital bits wererepresented by micrometre-sized pits etched into theplastic and scanned for playback by a laser diode in aCD player. In retrospect, this new technology deservedto be launched with its own musical fanfare, but thefirst CD released, in 1982, was the commercial album52nd Street by rock artist Billy Joel.In the mid-1990s the CD’s capacity of 74 minutes ofmusic was greatly extended via digital versatile discsor digital video discs (DVDs) that can hold an entirefeature-length film. In 2009 Blu-ray discs (BDs) ap -peared as a new standard that can hold up to 50 gigabytes,which is sufficient to store a film at exceptionallyhigh resolution. The difference between these formatsis the laser wavelengths used to write and read them –780 nm for CDs, 650 nm for DVDs and 405 nm forBDs. The shorter wavelengths give smaller diffractionlimitedlaser spots, which allow more data to be fittedinto a given space.Although the download revolution has led to a de -cline in CD sales – 27% of music revenue last year wasfrom digital downloads – lasers remain essential to ourPhysics World May 2010

physicsworld.comThe laser at 50: A cultural historyGIPhotoStock/Science Photo LibraryNIH/Custom Medical Stock Photo/Science Photo Libraryentertainment. They carry music, films and everythingthat streams over or can be downloaded via the Inter -net and telecoms channels, depositing them into ourcomputers, smart phones and other digital devices.Physics World May 2010Death rays...Among the films that you might choose to downloadover the Internet are some in which lasers are portrayedas destructive devices, encouraging negativeconnotations. In the film Real Genius (1985), a scientistco-opts two brilliant young students to develop anairborne laser assassination weapon for the militaryand the CIA. The students avenge themselves by sabotagingthe laser to heat a huge vat of popcorn, produ -cing a tsunami of popped kernels that bursts openthe scientist’s house. The film RoboCop (1987) showsa news report that a malfunctioning US laser in orbitaround the Earth has wiped out part of SouthernCalifornia. This was a satirical response to the idea oflaser weapons in space, a hotly pursued dream for thenUS President Ronald Reagan.The US military was thinking about laser weaponswell before high-power industrial CO 2 lasers were meltingmetal. As the Cold War raised fears of all-out conflictwith the Soviet Union, the potential for a newhi-tech weapon stimulated the Pentagon to fund laserresearch even before Maiman’s result. But it was dif -ficult to generate enough beam power within a reasonablysized device – early CO 2 lasers with kilowattoutputs were too unwieldy for the battlefield. Even -tually, in 1980, the Mid-Infrared Advanced ChemicalLaser reached pulsed powers of megawatts, but was stilla massive device. Even worse, absorption and otheratmospheric effects made its beam ineffective by thetime it reached its target.That would not be a concern, however, for lasers firedin space to destroy nuclear-tipped intercontinentalballistic missiles (ICBMs) before they re-entered theatmosphere. Development of suitably powerful laserssuch as those emitting X-rays became part of the multibillion-dollaranti-ICBM Strategic Defense Initiative(SDI) proposed by Reagan in 1983. Known to the generalpublic and even to scientists and the government as“Star Wars” after the film, the scheme had an undeniablyscience-fiction flavour. But the US weaponizationof space was never realized – by the 1990s technical difficultiesand the fall of the Soviet Union had turnedlaser-weapons development elsewhere. Now it is mostlydirected towards smaller weapons such as airbornelasers that have a range of hundreds of kilometres....and life raysWhile the morality associated with weapons may bedebatable, lasers are used in many other areas that areundeniably good, such as medicine. The first medicaluse of a laser was in 1961, when doctors at ColumbiaUniversity Medical Center in New York destroyed atumour on a patient’s retina with a ruby laser. Becausea laser beam can enter the eye without injury, ophthalmologyhas benefited in particular from laser methods,but their versatility has also led to laser diagnosis andtreatment in other medical areas.Using CO 2 and other types of lasers with varied wavelengths,power levels and pulse rates, doctors can preciselyvaporize tissue, and can also cut tissue whilesimultaneously cauterizing it to reduce surgical trauma.One example of medical use is LASIK (laser-assistedin situ keratomileusis) surgery in which a laser beamreshapes the cornea to correct faulty vision. By 2007,some 17 million people worldwide had undergonethe procedure.In dermatology, lasers are routinely used to treatbenign and malignant skin tumours, and also to providecosmetic improvements such as removing birthmarksor unwanted tattoos. Other medical uses are asdiverse as treating inaccessible brain tumours with laserlight guided by a fibre-optic cable, reconstructing damagedor obstructed fallopian tubes and treating her -niated discs to relieve lower-back pain, a procedurecarried out on 500 000 patients per year in the US.Yet another noble aim of using lasers is in basic andapplied research. One notable example is the NationalIgnition Facility (NIF) at the Lawrence Livermore Na -tional Laboratory in California. NIF’s 192 ultravioletlaser beams, housed in a stadium-sized, 10-storeybuilding, are designed to deliver a brief laser pulsemeasured in hundreds of terawatts into a millimetrescale,deutrium-filled pellet. This is expected to createMake light workThe diverse uses oflasers include (leftto right) bar-codescanning, transmittinginformation via opticalfibres, Blu-ray discsand laser eye surgery.19

The laser at 50: A cultural historyphysicsworld.comSee the lightArtist Hiro Yamagatalinked sciencewith art at his“Photon 999”exhibition, wheremultiple lasersystems immersedthe viewers in amoving-light show.20conditions like those inside a star or a nuclear ex plo -sion, allowing the study of both astrophysical processesand nuclear weapons.A more widely publicized goal is to induce the hy -drogen nuclei to fuse into helium, as happens insidethe Sun, to produce an enormous energy output. Aftersome 60 years of effort using varied approaches, scientistshave yet to achieve fusion power that producesmore energy than a power plant would need to operate.If laser fusion were to successfully provide this limitless,non-polluting energy source, that would more thanjustify the overruns that have brought the cost of NIFto $3.5bn. Although some critics consider laser fusiona long shot, recent work at NIF has realized some of itsinitial steps, increasing the odds for successful fusion.Popular culture is also hopeful about the role of lasersin “green” power. Although the film Chain Reaction(1996) badly scrambles the science, it does show alaser releasing vast amounts of clean energy from thehydrogen in water. In Spider-Man 2 (2004), physicistDr Octavius uses lasers to initiate hydrogen fusion thatwill supposedly help humanity; unfortunately, this isno advertisement for the benefits of fusion power, forthe reaction runs wild and destroys his lab.Lasers in high and not-so-high cultureSituated between the ultra-powerful lasers meant toexcite fusion and the low-power units at checkout countersare lasers with mid-range powers that can providehighly visible applications in art and entertainment, asartists quickly realized. A major exhibit of laser art washeld at the Cincinnati Museum of Art as early as 1969,and in 1971 a sculpture made of laser beams was partof the noted “Art and Technology” show at the Los An -geles County Museum of Art. In 1970 the well-knownUS artist Bruce Nauman presented “Making Faces”, aseries of laser hologram self-portraits, at New YorkCity’s Finch College Museum of Art.Other artists followed suit in galleries and museums,but lasers have been most evident in larger venues.Beginning in the late 1960s, beam-scanning systemswere invented that allowed laser beams to dynamicallyfollow music and trace intricate patterns in space. Thisled to spectacular shows such as that at the Expo ’70World’s Fair in Osaka, Japan, and those in planetar -Hiro Yamagataiums. A favourite type featured “space” music, like thatfrom Star Wars, accompanied by laser effects.Rock concerts by Pink Floyd and other groups werealso known for their laser shows, though these are nowtightly regulated because of safety issues. But spec -tacular works of laser art continue to be mounted, forexample the outdoor installations “Photon 999” (2001)and “Quantum Field X3” (2004) created at the Gug -gen heim Museum in Bilbao, Spain, by Japanese-bornartist Hiro Yamagata, and the collaborative Hope StreetProject, installed in 2008. This linked together twomajor cathedrals in Liverpool, UK, by intense laserbeams – one highly visible green beam and also severalinvisible ones – that carried voices and generated ambientmusic to be heard at both sites.After 50 years, striking laser displays can still evokeawe, and lasers still carry a science-fiction-ish aura, asdemonstrated by hobbyists who fashion mock ray-gunsfrom blue laser diodes. Unfortunately, the mystiquealso attaches itself to products such as the so-calledquantum healing cold laser, whose grandiose title usesscientific jargon to impress would-be customers. Itsmaker, Scalar Wave Lasers, asserts that its 16 red andinfrared laser diodes provide substantial health andrejuvenation benefits. Even the word “laser” has beenappropriated to suggest speed or power, such as for thepopular Laser class of small sailboats and the Chryslerand Plymouth Laser sports cars sold from the mid-1980s to the early 1990s.The laser’s distinctive properties have also becomeenshrined in language. A search of the massive Lexis -Nexis Academic research database (which encompassesthousands of newspapers, wire services, broadcast transcriptsand other sources) covering the last two yearsyields nearly 400 references to phrases such as “laserlikefocus” (appearing often enough to be a cliché),“laser-like precision”, “laser-like clarity” and, in a des -cription of Rus sian Prime Minister Vladimir Putin ex -pressing his displeasure with a particular businessman,“laser-like stare”.Lasers have significantly influenced both daily lifeand science. With masers, they have been part of re -search, including work outside laser science itself, thathas contributed to more than 10 Nobel prizes, beginningwith the 1964 physics prize awarded to CharlesTownes with Alex sandr Prokhorov and Nicolay Basovfor their fundamental work on lasers. Other relatedNobel-prize research includes the invention of holographyand the creation of the first Bose– Einstein condensate,which was made by laser cooling a cloud ofatoms to ultra-low temperatures. Also, in dozens ofapplications from Raman spectro scopy to adaptiveoptics for astronomical telescopes, lasers continuallycontribute to how science is done. They are also essentialfor research in such emerging fields as quantumentanglement and slow light.It is a tribute to the scientific imagination of the laserpioneers, as well as to the literary imagination of wri -ters such as H G Wells, that an old science-fiction ideahas come so fully to life. But not even imaginative wri -ters foresaw that Maiman’s invention would change themusic business, create glowing art and operate in su -per markets across the globe. In the cultural impact ofthe laser, at least, truth really does outdo fiction.Physics World May 2010

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physicsworld.comThe laser at 50: The early yearsTheodore Harold MaimanAnd then there was lightThe laser’s early years were full of scientific creativity, public-relations spin and intense rivalry.Pauline Rigby describes how a then little-known scientist became the first person to design and build aworking laser – and how the competitiveness of that period persists to this dayThe race to make a laser began with Bell Laboratories.In the late 1950s the then Bell Telephone Laboratorieswas a well-funded research institute in Murray Hill,New Jersey, that already had a string of high-profileachievements to its name – including the transistor,which was invented in 1947 by John Bardeen, WalterBrattain and William Shockley. A few years later, aBell Labs re search group led by Charles Townes proposeda device that could produce and amplify electromagneticradiation in the microwave region of thespectrum. By 1953 the researchers had turned theirtheory into a working device, which they called a maserPhysics World May 2010– an acronym for microwave amplification by stimulatedemission of radiation. And in December 1958,Townes and his brother-in-law Arthur Schawlow wrotea famous paper (Physical Review 112 1940) describinghow the maser concept could be extended into theoptical regime, to make the first “infrared and opticalmaser” – in other words, a laser.So if there was going to be a race to build a laser, itwas a race that Bell Labs fully expected to win. But thefavourites quickly faced competition. Townes had beenconsulting at Bell Labs, but by the time his 1958 paperwas published he was back at Columbia University.Pauline Rigby is afreelance technologywriter based in theCotswolds, UK,e-mail pauline@opticalreflection.com23

The laser at 50: The early yearsphysicsworld.comFirst light: key dates in the invention of the laser15 December 1958 Arthur Schawlow and Charles Townes’ paper on “Infrared andoptical masers” appears (Phys. Rev. 112 1940)15 July 1959 Ali Javan publishes his proposal for making a gas laser (Phys. Rev. Lett.3 87)16 May 1960 Theodore Maiman observes pulsed lasing in pink ruby7 July 1960 Hughes Research Laboratories holds a press conference announcingMaiman’s laser20 July 1960 Maiman improves his ruby laser design and observes a pencil beam1 August 1960 Donald Nelson and colleagues at Bell Labs create a pulsed laserbeam from a ruby rod in a configuration similar to the one shown in pressphotographs of Maiman’s device6 August 1960 Maiman’s short letter “Stimulated optical radiation in ruby” ispublished (Nature 187 493)25 September 1960 Nelson and his team at Bell Labs flash a laser beam 25 milesfrom Crawford Hill to Murray Hill in New Jersey1 October 1960 Publication of Bell Labs’ ruby-laser paper (Phys. Rev. Lett. 5 303)5 October 1960 Bell Labs holds a press conference to announce its ruby laser12 December 1960 Javan and his team create the first gas laser30 January 1961 Javan’s paper on the gas laser appears (Phys. Rev. Lett. 6 106)31 January 1961 Bell Labs holds a press conference announcing the gas laser1961 Willard Boyle and Nelson create the first continuously operating ruby laser(Appl. Opt. 1 181)There, he began trying to make a laser using hot potassiumvapour – the medium described in the paper.Schawlow decided not to go into direct competitionwith Townes, and so selected ruby as an alternativepotential laser material, in part because Bell Labs hada good supply of synthetic rubies for maser research. Asecond Bell Labs team was studying visible emissionsfrom calcium-fluoride crystals doped with various rareearthmetals; a third, led by Townes’ former graduatestudent Ali Javan, was trying to build a gas laser usinghelium and neon.Beyond Bell Labs, other research institutes aroundthe world soon joined the race. In the US alone, therewere major research efforts going on at General Elec -tric, IBM, the Massachusetts Institute of Tech no logy’sLincoln Laboratory, RCA Labor at ories and West -inghouse Research. Another strong contender wasTownes’ former student Gordon Gould, who had independentlycome up with an idea for a sodium-vapourbaseddevice in 1957 – coining the term “laser” in theprocess. The following year Gould abandoned his PhDthesis and joined TRG, a private research company,The dark horse in the laser race wasTheodore Harold Mai man, anengineer by training who hadswitched to physics. In the quest tomake a laser, Maiman’s engineeringand physics experience wouldboth prove essential24so he could pursue his ideas. The company won a $1mgrant from the defence-related Advanced Re searchProjects Agency to work on the laser, but Gould wasbarred from taking part in the project because it wasclassified and he could not get security clearance.Late entryThe dark horse in the race was Theodore Harold Mai -man, who was then at Hughes Research Labor atories,the research arm of the Hughes Aircraft Company.Mai man was an engineer by training who had switchedto physics, studying the fine-structure splittings ofenergy levels in excited helium atoms at StanfordUniversity under Willis Lamb, who had won the 1955Nobel Prize for Physics. In the quest to make a laser,Maiman’s engineering and physics experience wouldboth prove essential.Maiman entered the race late, at the point whenmany researchers appeared to be on the point of givingup. Moreover, Hughes took some persuading tofund his interest in lasers. After all, it was in the aerospacebusiness. What would it do with a beam of light?However, Hughes did have a contract with the USArmy Corps of Engineers to make a maser. This turnedout to be Maiman’s opportunity.“Ted struck an agreement with Hughes,” Maiman’swife Kathleen recalled during an interview withPhysics World (Maiman died in 2007, aged 79). “If hewas successful in delivering the maser for the ArmyCorps of En gin eers, he would be given nine monthsand $50 000 to actually make coherent light. He wentto work to make the maser more practical, and took itfrom 5000 lbs to 2.5 lbs and also improved the line -width. Because of that, he was able to do a dedicatedproject on the laser.”Like Schawlow, Maiman started investigating rubyas a laser material because he was familiar with its propertiesfrom his maser work. Ruby is a crystal of aluminiumoxide containing a tiny amount of chromium– about 0.5% in the case of gemstone ruby, and about a10th of that in “pink” ruby used for industrial applications.As well as emitting microwaves, pink ruby alsostrongly absorbs light in the green part of the opticalspectrum, and fluoresces in the red. Such behaviour isa consequence of pink ruby’s three-level energy system(figure 1). When pink ruby absorbs green light, electronsare promoted from the ground state to a higherenergy level. The electrons then lose energy throughthermal relaxation (lattice vibrations), ending up in anintermediate, meta stable energy level. Decay from thismeta stable level back to the ground state is respon siblefor the red fluorescence, and this was the transitionMai man hoped to use in his laser.But in September 1959, shortly after Maiman startedhis project, Schawlow publicly declared that pink rubycould not possibly work as a laser. For stimulated emissionto occur, more electrons need to reside in the up -per energy level than a lower one – a condition knownas a population inversion. Schawlow argued that itwould be too difficult to achieve this inversion in athree-level system because the ground state in such asystem is usually full of electrons. He maintained thatit would be much easier to achieve population inversionin a four-level system containing an empty energyPhysics World May 2010

physicsworld.comThe laser at 50: The early years1 A three-level system in pink rubyexcited statespumping lightthermalrelaxationmetastable levelslaser transition694.3 nmground stateChromium ions in pink ruby absorb light in the green and blue regionsof the spectrum. In the presence of this pumping light, electrons in theions are promoted to excited states, where they then rapidly decay toone of two metastable levels. The unusually long lifetime (about 4 ms)of these levels allows more than half of the available electrons to buildup there, creating a population inversion – the condition needed forlasing to occur.level between the ground state and the meta stablelevel (figure 2).With respected scientists counselling against pinkruby, Maiman’s employer was reluctant to continuefunding his idea, which it was doing out of its ownpocket. But Maiman was not deterred, because it wasclear from Schawlow’s comments that he was consideringa cryogenically cooled laser. As Maiman wrote inhis memoirs, The Laser Odyssey (2000 Laser Press),“the possibility of room-temperature operation hadbeen dismissed out of hand”.Maiman’s only moment of real doubt came when ascientist he had personally trained, Irwin Wieder, publisheda paper claiming that the quantum efficiency ofruby fluorescence was just 1% – in other words, onlyone absorbed photon in 100 results in an emitted photon(Review Scientific Instruments 30 995). If true, thiswould mean it would be impossible to pump enoughenergy into ruby to achieve stimulated emission. Butinstead of giving up, Maiman devised experiments todetermine why the quantum efficiency of ruby fluorescenceshould be so low, in order to guide his searchfor a suitable alternative. Finding no an swers, in the endhe made his own measurements on ruby, which showedthat the quantum efficiency was actually closer to 75%.This was typical of Maiman’s approach to research,according to Kathleen. “Ted was a very, very carefulscientist, and very precise in his work,” she says. “Hedidn’t take anything at face value. He calculated andrecalculated until he was absolutely sure it was correct.”Even with 75% quantum efficiency, Maiman’s calculationsindicated that he would need a very bright pumplight to deliver enough energy to the pink ruby toachieve stimulated emission. His “eureka” momentcame from reading an article about photographicstrobe lamps, which could achieve “brightness tem -peratures” of 8000 K, albeit only for a moment. (Bright -ness temperature is a measure of radiation intensityin terms of the temperature of a hypothetical blackbody. For reference, the Sun’s brightness temperaturePhysics World May 20102 Three- and four-level laser systemsshort-livedmetastablepumpfast decaylasing transitionshort-livedmetastableshort-livedpumpground stateground stateIn a three-level laser system, more than half of the particles in the laser medium must bepumped out of the ground state and into the metastable state (via the short-lived excited state)for a population inversion to occur. Achieving this requires a very intense pumping light.Population inversion in a four-level laser system, in contrast, occurs whenever the population ofthe metastable state exceeds that of the lower short-lived state. Hence, only a few particlesneed to be excited before stimulated emission can take place.is about 5500 K.) This was a departure from themethods of other researchers, who were working withcontinuous illumination.The next problem was how to concentrate the lightonto the ruby. According to Maiman’s calculations,lamps shaped like straight tubes – which could be positionedat the focus of an elliptical mirror – would notbe powerful enough. The most powerful strobe lampsof the time had a spiral shape, and so he decided to“stick with what was available”. The spiral shape of thelamp meant he could not use a simple lens to focus thelight onto the ruby crystal, so Maiman positioned theruby as close to the light source as possible. This meantputting the 1 × 2 cm ruby inside the lamp spiral, andplacing the entire arrangement inside a polished aluminiumcylinder to help gather the light (see image onpage 23). Thick silver coatings on the ends of the rubywere used to create the optical cavity, leaving a smallhole in the coating at one end to allow light to escape.On 16 May 1960 his work paid off. Maiman and hisassistant Irnee d’Haenens observed the first evidenceof laser action: a large decrease in the ruby’s fluorescencelifetime as seen in the device’s spectral output,once the flash-lamp input was increased to more than950 V. Below this threshold, the only light-emissionmechanism is normal fluorescence. Above it, however,stimulated emission becomes the dominant process,and the metastable energy level empties much faster,leading to a reduction in the fluorescence lifetime.In a second experiment performed a few days later,Maiman used a spectrograph to measure narrowing inspectral linewidth above the laser threshold – anothercharacteristic of stimulated emission. Furthermore,pink ruby’s red fluorescence consists of two closelyspaced spectral lines, and Maiman had calculated thatonly one of these lines would actually lase – and that isexactly what he saw.Into the limelightHaving fought to obtain funding to carry out his re -search in the first place, Maiman then faced an uphillstruggle to get his discovery acknowledged. When hesubmitted a paper to Physical Review Letters, it was re -jected as “just another maser paper”. Maiman quicklypenned a shorter, 300-word version of his article andfast decayfast decaylasing transition25

The laser at 50: The early yearsphysicsworld.comHughes Research Laboratoriesfrom an unknown working for an aircraft company. Thebiggest problem, however, was that Mai man’s detailedscientific results were not available for scrutiny whenthe press conference was held. Worse, the Nature paper– when it was finally published on 6 August – was sobrief that it failed to convince his critics.Despite the uncertainty, Hughes’ press conferenceinfused the laser research community with new vigourand new funding. Scientists around the world returnedto their work with fresh conviction that it was actuallypossible to make a laser. In fact, the concept and designof Maiman’s laser proved so simple that it was only amatter of weeks before his results had been reproducedby several other researchers – most prominently those atBell Labs, who demonstrated a pencil beam from theirruby device on 1 August 1960. Taking their cue from thepublicity photograph showing “not the first” laser (seeimage left), the Bell Labs researchers used a 5 cm-longruby rod with an identical model of strobe lamp.By then, Maiman had also observed a pencil beam,thanks to three new ruby crystals that had been speciallygrown to the dimensions he required (the ruby inthe first laser, by contrast, had been cut from a largerboule). On the day the new crystals arrived, 20 July1960, Maiman inserted them into his device andobserved sharp threshold behaviour and a bright spoton the wall.Better than thereal thing?The photographissued at the 7 July1960 Hughes pressconference showingMaiman with a laterprototype laser – notthe first one– ledto melodramaticnewspaper headlinesand confusion amongother researchers.26sent it to Nature, where it was accepted (187 493). Be -fore it could be published, however, Hughes decided tohold a press conference. As a scientist, Maiman wantedto publish first, but Hughes was becoming nervous: theBell Labs groups might be really close, and there wouldbe no prize for second place.The Hughes public-relations machine swung intoaction ahead of the press conference, which it hadscheduled for 7 July 1960. The photographer hired totake the shots was not impressed by the first laser – itwas too small (see image on page 23). Looking aroundthe lab, he picked up a later prototype with a mediumsizedflash lamp and 5 cm-long ruby rod, telling Mai -man to “Hold this in front of your face and I know thiswill be picked up by every news outlet, but if we printthis, this first laser, it won’t go anywhere.” The photo -grapher was right. The day after the press conferenceall the major newspapers carried the photograph –along with, in one case, the melodramatic headline“LA man discovers science-fiction death ray”.Within the academic community, though, there was acertain amount of scepticism and confusion about whatMaiman had achieved. The optical quality of the crystalin his first laser was poor and so he had not ob servedthe characteristic “pencil beam”. Instead, his early re -sults were based on sensitive spectroscopic measurements.Maiman also faced some degree of prejudice:people expected the advance to come from Bell Labsor one of the other well-funded research efforts, notStill controversialIn the years that followed, Bell Labs researchersachieved many laser “firsts”, including the first gaslaser, which Javan and co-workers demonstrated successfullyin December 1960. Other successes includedthe first continuously operating ruby laser, made byWillard Boyle and Donald Nelson in 1961; the first carbon-dioxidelaser, invented by Kumar Patel in 1964;and a string of other innovations, including refinementsto the now-ubiquitous semiconductor diode laser.Maiman, for his part, left Hughes in 1961 to join aventure-capital-funded start-up called Quanatron,where he was in charge of laser activities. The followingyear Union Carbide provided the funds to set up his labas an independent business. Thus Maiman becamepresident of the newly formed Korad Corporation,which invented the Q-switched laser and became a supplierof the highest power lasers in the industry.Over the laser’s 50-year history, Maiman’s place asinventor of the laser has sometimes been acknow -ledged. In 1984 he was inducted into the National In -ventors Hall of Fame – meeting Kathleen, who becamehis second wife, on the flight home afterwards. Mostsignificantly, in 1987 he was awarded the Japan Prize,which is often considered the Eastern equivalent ofthe Nobel.But at other times, Maiman felt his role was downplayed.It was Townes who shared the 1964 Nobel Prizefor Physics with two Russian theorists, Nicolay Basovand Aleksandr Prokhorov, for “contributions to fundamentalwork in quantum electronics leading to thedevelopment of the maser–laser principle”. And in1998, Bell Labs honoured Townes’ work again with amajor celebration to mark “the 40th anniversary of thelaser” – a reference to the 1958 “optical maser” paper,rather than to the invention of a working device twoPhysics World May 2010

physicsworld.comThe uncomfortable truth is thatfor some of the people involved,even 50 years after the fact,the invention of the laser isstill controversialyears later.For Maiman, the lack of recognition hurt, and itprompted him to write a memoir presenting his sideof the story. “Ted wrote his book because he felt thathis place in history was not being properly addressed,”explains Kathleen. “And I still offer [anyone who asks]The Laser Odyssey because it was directly from him andit’s correct.”In the book, Maiman hits back at his critics, assertingthat Bell Labs has little claim on inventing the laserbecause its proposal never worked: no body has everbeen able to make a potassium-pumped potassiumvapourlaser as described in Schawlow and Townes’1958 paper, and the patent based upon it never earnedany money. Indeed, Maiman attributes his success tothe fact that he did not follow the teachings of Schaw -low and Townes; if he had, he would never have consideredpink ruby as a suitable laser medium.Maiman’s attitude may sound harsh, but the uncomfortabletruth is that for some of the people involved,even 50 years after the fact, the invention of the laseris still controversial. In a feature article published inthe January issue of Physics Today magazine, Nelson,Ro bert Collins and Wolfgang Kaiser – three Bell Labsresearchers who worked on early laser projects – des -cribe “the work at Bell Labs in the summer of 1960 thatled to the creation of the first ruby laser”.Those claims disconcert Kathleen, who believes thatMaiman’s position as creator of the first laser is beyonddispute. “The Bell Labs scientists had a photo of Ted’slaser from the newspaper [and] the account that hispink ruby crystal worked,” she says. “And Schawlowhad obtained from Ted a copy of his unpublished submissionto Physical Review Letters describing the constructionof his laser. All of these facts combined wouldclearly mean that any subsequent construction andoperation of a laser at Bell Labs was purely imitatingwhat Ted had already done.”Kathleen still keeps a notebook from the day, 16 May1960, when Maiman made his laser breakthrough. Sheacknowledges there have been some “sour grapes”over the years. Yet she has even stronger feelings aboutthe positive contribution Maiman made to society.“I had great appreciation for Ted Maiman the man, aloving husband and a delightful companion,” she says.“But what I’m really finding extraordinary right now isTed Maiman the scientist. I’m beginning to appreciatehow there are moments in the history of humanitywhen an advance occurs that is so extraordinary andun expected that the world for better or worse ischanged forever. I think the invention of the laser on16 May 1960 marks one of these times.”Physics World May 2010New from OxfordThe Many Worlds of Hugh Everett IIIMultiple Universes, Mutual Assured Destruction,and the Meltdown of a Nuclear FamilyPeter ByrneQuantum Electronics for Atomic PhysicsWarren Nagourney‘This is a well-written and readable introduction toquantum electronics which treats topics not usually foundin traditional texts. Nagourney has put together what couldbecome a standard book in the field.’- Ifan Hughes, Durham UniversityOxford Handbook of Nanoscience andTechnologyThree-Volume SetLectures on LightNonlinear and Quantum Optics using the DensityMatrixStatistical MechanicsTheory and Molecular SimulationEdited by A.V. Narlikar and Y.Y. FuThis is an agenda-setting and high-profile book thatpresents an authoritative and cutting-edge analysis ofnanoscience and technology.Stephen C. Rand‘A textbook which thoroughly introduces the density matrixformalism and applies it to a range of topics of currentinterest constitutes a "missing link" among quantum opticstextbooks.’- Christoph Becher, Saarland University, GermanyMay 2010 | 978-0-19-957487-2 | Hardback | £39.95Mark Tuckerman‘This book has the potential to become the definitivebiography of one of the finest minds of the twentiethcentury.’- David Deutsch FRS, Oxford UniversityMay 2010 | 978-0-19-955227-6 | Hardback | £25.00April 2010 | 978-0-19-953262-9 | Hardback | £45.00April 2010 | 978-0-19-957443-8 | Pack | £299.00Atomic Force MicroscopyPeter Eaton and Paul WestA very practical guide which will demystify Atomic ForceMicroscopy for the reader, making it easy to understand,and to use.March 2010 | 978-0-19-957045-4 | Hardback | £55.00Treats both basic principles in classical and quantumstatistical mechanics as well as modern computationalmethods, providing both model and real-worldexamples.February 2010 | 978-0-19-852526-4 | Hardback | £47.99PHONE: +44 (0) 01865 353250EMAIL: science.books.uk@oup.com24-hour credit card hotline: +44 (0)1536 454534Visit our website: www.oup.com/uk127

The laser at 50: Laser fusionphysicsworld.comNational Ignition Facility28Physics World May 2010

physicsworld.comThe laser at 50: Laser fusionFusion’s brightnew dawnAs we celebrate 50 years of the laser, a milestone looms inthe world of laser fusion. Mike Dunne describes howachieving ignition – fusion’s break-even point – with theworld’s largest laser will transform the search forabundant, carbon-free electricityPhysics World May 2010Ready, aim, fireA view inside thetarget chamber atthe US NationalIgnition Facility.Three days after Theodore Maiman demonstrated thefirst ruby laser at his laboratory in Malibu, California,in May 1960, a scientist a few miles away at the Law -rence Livermore National Laboratory came up with anidea for using lasers to harness the power source of thestars. Although details of Maiman’s device would notemerge for several weeks, scientists already knew that alaser’s ability to concentrate energy in time and spacewould be unprecedented. Might it be possible, theLiver more scientist wondered, to use lasers to fuse smallatoms together to create a heavier, more stable atom –releasing huge amounts of energy in the process?Thanks to the levels of secrecy prevalent at thetime concerning atomic matters, it would be another12 years before the scientist in question, John Nuckolls,articulated his ideas about laser fusion for the broaderscientific community. Writing in Nature, Nuckolls andhis colleagues explained that in order for their schemeto work, a large-scale laser had to be built – one thatcould compress and heat the fusion fuel to a temperatureof 10 8 K and densities 1000 times that of liquids,con ditions that surpass even those found at the centreof the Sun.Nuckolls’ team predicted that a laser with an energyof 1 kJ and a pulse length of a few nanoseconds wouldbe sufficient to initiate the process, although a muchlarger laser (a few megajoules, it was estimated) wouldbe required to produce a substantial energy output. Sci -entific excitement over this idea – coupled with a successionof energy crises in the 1970s and 1980s – led tothe construction of a series of increasingly large lasersto test the concept. Unfortunately, these experimentsproved that the journey would be much harder than predicted:the threshold itself was likely at the megajoulelevel, thanks to the need to overcome a range of instabilitiesthat hampered efforts to couple laser energy tothe fuel and then compress it to the required densities.Yet after years of intermittent successes and setbacks,we are finally entering a truly exciting period in theworld of laser fusion. The past decade has seen un -precedented sums of money invested in the field, withthe principal aim of demonstrating, once and for all,that the science of laser fusion really works. The re -cently completed US National Ignition Facility (NIF),Mike Dunneis Director of theCentral Laser Facilityat the STFCRutherford AppletonLaboratory in Didcot,Oxfordshire, UK,e-mail mike.dunne@stfc.ac.uk29

The laser at 50: Laser fusionphysicsworld.comThe National Ignition FacilityThe National Ignition Facility (NIF) is the world’s largest laser. Located at California’sLawrence Livermore National Laboratory, it covers 70 000 m 2 (roughly two footballpitches) and contains 8000 large optical units (each up to 1 m in diameter) and30 000 smaller optics. These and other components are contained in approximately6000 modular units that can be replaced quickly when necessary to ensurecontinuous operation of the facility.Together, the facility’s 192 laser beams can deliver 1.8 MJ of energy with acombined power of 500 TW (500 × 10 12 W). This is about 40 times more power thanthe average consumption of the entire world, and a few times greater than the powerof all the sunlight falling on the Earth. Of course, this power only lasts for a fewnanoseconds, so it contains only a trivial amount of energy. But when this energy isdelivered through multiple traversals of the 100 m long hall (see image above) andfocused down to millimetre scales at the centre of a 10 m diameter “target chamber”,it is enough to create shock waves with pressures of tens of millions of atmospheres.This pressure makes the fuel pellet implode, forcing the atoms of deuterium andtritium inside to fuse together. Getting it right requires a lot of effort; for example, thetarget chamber is held under vacuum to allow the lasers to be focused down to spotsjust 1 mm in diameter, and the fuel pellet itself has to be extremely round and smooth,since any imperfection is exponentially amplified in the course of the implosion.30located at the same lab where Nuckolls had his big idea50 years ago, is among the most tangible results of thiseffort (see box above). And a little over a year after NIFofficially opened, scientists there are now on the brinkof a breakthrough: crossing the required threshold forthe instigation of a self-sustaining fusion reaction, leadingto a net release of energy for the first time.The achievement of this 50-year-old goal – knowntechnically as “ignition” – will be a game-changingevent that will propel laser fusion from an elusive phenomenonof physics to a predictable, controllable, technologicalprocess ready to address one of society’s mostprofound challenges: finding an enduring, safe andenvironmentally sustainable source of energy. The NIFplan is to ensure that this milestone is reached withinthe next two years.Making a star in the labThe history of fusion can be traced back to 1920, whenFrancis William Aston discovered that four separatehydrogen nuclei are heavier than a single helium nuc -leus. This occurs because the stability of helium leadsto a lower overall rest mass. On the basis of this work,another British scientist, Arthur Eddington, proposedNational Ignition Facilitythat the Sun could get its energy from converting hy -drogen nuclei into helium nuclei, releasing just lessthan 1% of the mass as energy, according to Einstein’sfamous equation E = mc 2 . Then, in 1939, Hans Bethedistilled these facts into a quantitative theory of energyproduction in stars, which eventually won him the 1968Nobel Prize for Physics.Although the Sun and other stars generate fusionby using their gravitational energy to compress hydrogen(and subsequently heavier elements), for any terrestrialeffort it makes more sense to use a fuel sourcecomposed of deuterium and tritium. These isotopes ofhydrogen contain one and two neutrons, respectively(figure 1). They have the highest cross-section for fusionsince they have low charge (just a single proton each)and the proton and neutron(s) are not very tightlybound. In the basic fusion reaction, deuterium (D) andtritium (T) combine to form helium and a very energeticneutron: 2 D + 3 T → 4 He (3.5 MeV) + n (14.1 MeV)In order for this reaction to take place, the particlesneed to be moving at very high velocities to overcomethe Coulomb barrier, since the positive ions experiencean increasingly strong repulsive force as they get closerand closer together. This means that the fuel needs tobe heated to an incredible 10 8 K. Under these conditions,electrons are stripped from their parent nuclei,turning the fuel into a plasma.The need to create high-temperature plasmas forfusion to occur explains why fusion is not a processwe encounter in everyday life on Earth, and why it isso incredibly difficult to harness as a net source ofpower. On a positive note, this does introduce onemajor benefit: unlike nuclear fission, which can lead toan un controlled “chain reaction”, the fusion process isin herently safe since the fuel “wants” to be inert, andthus loses energy at any opportunity. And thanks to thestars, we know categorically that fusion works – we justneed to find an alternative to the Sun’s use of gravity toprovide the heating and confinement of our fuel.There are two principal routes to achieving confinement:we can either hold the plasma in a magnetic fieldwhile heating it using radio waves or particle beams; orwe can compress it to unprecedented densities usinglasers. The first approach is being pursued through theITER magnetic-confinement fusion experiment currentlybeing built in Cadarache, France, while the latteris being studied at handful of labs – including NIF –using some of the world’s largest lasers.How laser fusion worksThe laser route to fusion neatly combines two of Ein -stein’s most famous contributions to science: his explan -ation of stimulated emission; and his quantification ofthe equivalence of mass and energy. The basic ap proachis a repetitively cycled system in which ball-bearingsizedpellets of deuterium–tritium fuel (figure 2) areinjected into the centre of a large, empty chamber. Anumber of powerful laser beams are used to compressthe fuel to densities of 1000 g cm –3 , or about 100 timesthe density of lead, for a few millionths of a millionth ofa second (10 –12 s). Of course, this high-density fuel willsubsequently blow apart – but not instantaneously. Itwill persist at high densities on a timescale determinedby its inertia and characterized by the time taken for aPhysics World May 2010

physicsworld.comThe laser at 50: Laser fusion1 Getting it together2 On targetDnpnppnHeNational Ignition FacilityTnnpIn a nuclear-fusion reaction, molecules of deuterium and tritium –isotopes of hydrogen with one and two neutrons, respectively –combine to produce helium and an energetic neutron.nnThe fuel pellets used in laser fusion are ball-bearing-sized hollowspheres made of beryllium (shown here), plastic or high-densitycarbon. The pellets must be extremely round, with a very smoothsurface, since any irregularity will cause the laser beam to transferenergy to the fuel unevenly.sound wave to propagate across the imploded assembly.This “self-confinement” phenomenon has led tothe process being called “inertial-confinement fusion”,and it gives the system sufficient time to allow a substantialfraction of the fuel (typically 30%) to be convertedto helium and a neutron.The first fusion reaction produces a helium ion thatdeposits its energy in the neighbouring fuel, thus allowingthe high temperatures to be maintained and thefusion reaction to propagate through the fuel. The highenergyneutron, however, escapes, since it interacts onlyweakly with the charged plasma. The neutron’s energyis therefore carried into a thick “blanket” of materialsurrounding the interaction chamber, heating the blanketto about 1000 K. In a fusion power plant, the processwould be repeated about 10 times per second, and theheat would be used to drive an ad vanced gas-turbinecycle, thereby generating electricity.The physics underpinning laser fusion is actuallyquite well understood. Moreover, thanks to a series ofexperiments performed by UK and then US scientistsin the 1980s (see Physics World March p23), we knowthat ignition and energy production can be attainedhere on Earth if we have a sufficiently powerful driver.These experiments, which used the X-ray output of anexploding thermonuclear bomb to implode the pellets,can be viewed as the ultimate “swords into plough -shares” demonstration. What remains is to prove thata laser can be used as the driving source, and to demonstratethat the emitted fusion energy can be harnessedat a level compatible with a full-scale power plant.The deuterium in the fuel pellet is sourced fromwater, which naturally contains about one molecule ofD 2 O for every 6000 molecules of H 2 O. The tritium, incontrast, must be manufactured in situ by bombardinglithium-6 atoms with neutrons, thereby transmutingthe lithium into tritium and helium. Here, we can usea neat trick: if we construct the blanket surrounding thefuel pellet with lithium-6, we can use the neutrons producedin the fusion reaction to generate more tritium(as well as producing the heat for the electricity turbine).In practice, it is a little more complicated thanthis, because we have to ensure that there are enoughPhysics World May 2010excess neutrons to create a closed fuel cycle; however,this can be achieved by adding other materials (principallylithium-7, beryllium or lead) to the blanket.On the laser side, Nuckolls’ original predictions thata relatively small-scale laser would be sufficient to createthe required conditions turned out to be correctonly if there is freedom to drive the implosion at anarbitrarily high velocity. This is not possible due to vari -ous unstable, nonlinear processes in which the laser canset off electron or ion “waves” in the plasma, or causethe imploding fuel to break up prior to reaching highcompression. For example, when high-intensity lasersheat matter, they can resonantly drive an oscillationin the plasma, thus causing the light to scatter off theplasma wave and preventing the fuel from absorbingit efficiently. If the laser intensity is too low, however,then the pellet implosion is driven at such a low velo -city that any imperfections arising from surface roughnessor laser non-uniformities seed the growth ofhydrodynamic instabilities, leading to total break upof the imploding shell prior to full compression.It has taken many decades to adequately understandthese processes, and their existence has meant that alaser roughly 1000 times the scale originally envisagedby Nuckolls has to be used. The lasers at NIF – whichhave been performing re markably well in their initialphase of operation – are designed to mitigate the growthof these plasma and hydrodynamic instabilities. Muchattention has been paid to ensuring a sufficiently“smooth” laser beam, with control over its temporalprofile to allow quasi-isentropic compression of the fuelby launching a series of precisely tailored shocks.From fusion to electricityFusion physicists are so confident that NIF will be ableto “ignite” a self-sustaining fusion reaction that attentionis now turning to the endgame. The next problemis how to best harness the emitted neut rons in a mannercompatible with a robust, commercially vi able powerplant. Such a plant would operate conceptually like acar engine, with three key stages.In the first step, fuel – in the form of a ball-bearingsizedpellet of frozen hydrogen isotopes, held at tem -Physicists areso confidentthat NIF willbe able to“ignite” aself-sustainingfusion reactionthat attentionis now turningto the endgame31

The laser at 50: Laser fusionphysicsworld.comLaser technology for fusion powerThe National Ignition Facility (NIF) is designed toprovide the scientific evidence that large-scalelasers can ignite and burn a fusion fuel capsule,producing between 10 and 100 times more“fusion energy out” than the amount of “laserenergy in” required to start the reaction. In orderto harness this energy for a power source, thelasers at NIF would have to operate about10 times per second, with each beam deliveringan average power of 10–100 kW and a laserefficiency (defined as “electricity in” per “laserenergy out”) of about 10%. Such high levels arenot possible at NIF, where laser efficiencies areless than 1% and the average power isapproximately 1 W.However, existing laser technologies indicatethat there is room to improve on these figures.NIF uses flash-lamp technology to pump itsamplifiers – the devices that convert incoherent“conventional” light into a high-energy laserbeam via the process of stimulated emission.Diode-laser-pumped solid-state amplifiers, incontrast, have been shown to operate at up to100 kW with efficiencies more than 10%,LULIalthough they are currently optimized forcontinuous-wave operation, not pulsed. Thestate of the art for pulsed laser systems iscurrently at the kilowatt level. The image showsa pulsed laser system at France’s Laboratoirepour l’Utilisation des Lasers Intenses facility,viewed through the focusing and guiding opticsto the pumped amplifier head.Many designs now exist for the required levelof operation for a laser-fusion system. Looking atthe rate of progress of pulsed laser systems, andthe substantial funding being attracted to thisarea for a variety of applications, the next fiveyears are likely to see construction andoperation of a prototype beamline. As with NIF,multiple numbers of such beams would befocused onto a millimetre-scale fuel pellet.32pera tures of about 18 K – is injected into a multi-metrediametervacuum chamber. Next, a laser “piston” compressesthe fuel by heating the outer surface of thepellet to create a hot, spherically expanding gas. Inorder to conserve momentum, the rest of the pellet isforced to move rapidly inwards at velocities of morethan 10 5 m s –1 . The degree of compression achieved inthis process is similar to squashing a basket ball downto the size of a pea.In advanced schemes – analogous to a petrol engine– a separate laser is then used as a “spark plug” toignite the fuel at the instant of maximum compression.Adding in this extra laser could lead to a more efficient(higher gain) system, but it is not an essential requirement:if we compress the fuel enough, the compressionalone will generate enough heat to create a hot“spark” at the centre of the imploding fuel. When thetemperature is high enough, and enough mass hasbeen imploded to an appropriately high density, fusionis initiated in a self-sustaining manner. The heliumnucleus from one reaction heats the neighbouring fuel,while the neutron escapes to heat the external blanketto generate electricity.The final step occurs when the spent fuel is exhaustedout of the chamber. At this point the cycle repeats. Ina car engine, the fuel cycle is repeated about 50–100times per second. The repetition rate for laser fusionis lower: 10 times a second would be enough to produceelectricity on the gigawatt scale, comparable to thelargest coal, gas or fission power stations. However,that rate is simply not possible with NIF, which firesonly once every few hours. New technology is neededto convert the scientific demonstration on NIF into aconstantly cycling system that can generate electricity.One project that aims to bridge the gap betweenachieving ignition and building a practical fusion powerplant is the High Power laser Energy Research facility,or HiPER. Led by the UK and involving a 10-nationconsortium of researchers and funding bodies, HiPER’sgoal is to demonstrate the 10 Hz level of performanceof all the component technologies for power-plant-scaleoperation within the next 10 years. To do this, we hopeto draw on innovations that are taking place elsewherein laser science, including the high-repetition-rate technologyused in the welding and machining industry, andseveral ongoing high-power-laser research projects.One example of the latter is the Extreme Light Infra -structure (ELI) project, a 7750m effort led by theCzech Republic, Hungary and Ro mania (see pp12–13)that seeks to create laser pulses with peak powers ofup to a few hundred petawatts (about 10 17 W) usingthe same type of diode-pumped laser technology thatHiPER will require (see box above).Over the past few decades, lasers have developed atan incredibly fast pace, allowing fusion researchers totake advantage of rapid increases in power and efficiency.Using lasers also allows us to adopt a modular,maintainable and easily upgraded approach to powerplantdesign during HiPER’s second phase, in whichwe plan to build a facility that combines the scientificdemonstration of ignition at NIF with high-repetitionratelaser technology. This modular strategy shouldreduce the timescale for construction, increase powerplantavailability throughout its life, and ensure that wefind the most cost-efficient solution.At the same time as Europe is devoting resources toHiPER, US scientists are planning a similar journeywith the aptly named LIFE project (Laser InertialFusion Engine). Led by the scientists who worked onNIF, this project has the same goal as HiPER: todemonstrate the required high-repetition-rate technology,integrated into a power-plant-scale facility.Scientists in Japan, meanwhile, have well-defined plansfor demonstrating the “petrol engine” approach topower generation des cribed above. Thanks to theseefforts, it is looking in creasingly likely that reachingignition at NIF will remove the question of whetherlaser-fusion power will be achieved, to replace it withthe more political question of who is likely to deliverthe first working power plant.Towards a working power plantThe achievement of ignition at NIF will provide theultimate verification of the scientific basis of laserfusionenergy, marking the culmination of 50 years’effort. Yet the second milestone – a working fusionPhysics World May 2010

physicsworld.comThe laser at 50: Laser fusionpower plant – is the real goal, motivated by the demandfor a sustainable, low-carbon economy. As we havealready seen, the principal ingredients in fusion aredeuterium, which is found in water, and lithium, whichoccurs naturally in igneous rocks and some types ofclay, as well as in seawater. The Earth contains enoughof both ingredients to last for millennia. In fact, basedon current rates of electricity consumption in the UK,just one bathtub of water and the lithium from two laptopbatteries would provide enough electricity for anindividual’s entire lifetime.Furthermore, fusion produces no greenhouse-gasemissions and has a low environmental impact over thelife-cycle of a plant. The chief waste product is inerthelium gas, and the residual radioactivity at the plantitself should be manageable using conventional de -commissioning techniques over a period of 100 years.Fusion plants will have power outputs of as much as1–2 GW, making them ideally suited as large, centralfacilities on the existing electricity-grid infrastructure.Other benefits include the high-temperature environmentof the blanket, which could be used to generatehydrogen for fuel cells or even to desalinate water.These wider applications, as much as their electricityoutput, may be the crucial factor that will determinethe commercial viability of early fusion power plants,and thus the timescale for delivery of the first generationof facilities.In the meantime, laser facilities used in the pursuitof fusion can also be exploited for pure research. Thetopics range from studies of astrophysical processes suchas nucleosynthesis, cosmic-ray generation, proto-stellarjets and planetary-nebulae formation, to the re searchinto the cores of gas-giant planets and the origins ofthe Earth’s magnetic field. The lasers could also underpina host of fundamental studies in areas as di verse asatomic physics, nuclear science, turbulence and the creationof macroscopic quantities of relativistic matter.Perhaps just as importantly, the component technologiesused in fusion research – not least the highlyefficient, high-power lasers themselves – open up a widerange of spin-off opportunities. These range from secur -ity screening for nuclear materials at ports and the productionof medical radioisotopes to the treatment ofdeep-seated tumours via particle-beam therapy, theprocessing of materials for the aerospace industry andeven the development of next-generation light sources.Pursuing a future energy source based on lasers stillfaces huge technological challenges in advanced ma -terials, micro-scale engineering, laser technology andintegrated power-plant systems. But the wider marketfor the high peak-power, high average-power laser systemsallows the fusion field to build from a well-developedin dustrial base, and to borrow advances fromother projects to accelerate the timescale to delivery.We have been waiting 50 years for the scientific proofthat controlled fusion works. Now that this proofis almost upon us, we need to make sure we capitalizeon it to ensure that we do not have to wait a further50 years to see it used.Pursuing afuture energysource basedon lasers stillfaces hugetechnologicalchallengesThe Tunability You Want.The Power and Control You Need.Put the power of New Focus into your BEC experiment and gain thepower, control and ease-of-use you desire. The combination of our NewFocus Vortex II or Velocity ® laser with our new VAMP tapered amplifierdelivers more power and precision, tunability and control than ever before.The result is an unsurpassed BEC solution with clean solid tuning from asingle seed laser, fiber coupled input option, and WIFI connectivity forease-of-use along with:• 100 GHz or 8000 GHz of mode hop free tuning• Narrow line-width unaltered after amplification• >1 W tunable light• Center wavelength from 760 nm to 980 nmFind out more by calling us. You may also visit us at www.newport.com/newfocusBEC for more information.BelgiumTel: +32 (0)0800-11 257FranceTel: +33 (0)1.60.91.68.68Germany / Austria / SwitzerlandTel: +49 (0) 61 51 / 708 – 0NetherlandsTel: +31 (0)30 659 21 11United Kingdom / IrelandTel: +44 (0)1235 432710© 2010 Newport Corporation.www.newfocus.comAD-041010-ENPhysics World May 201033

ilio Segrè Visual Archives; Mehau Kulyk/Science Photo Library; Martin Dohrn/Science Photo Library; Shuji Nakamura; Massachusetts Institute of Technology; Adam R ContosLight fantasticThe laser has become so ubiquitous that it would be impossible to acknowledge everyonewho has played a role in its success. As Roy Glauber said at the 2005 Nobel-prizebanquet, when it comes to lasers, “many hands make light work”. And he should know:the prize Glauber shared with fellow optics pioneers John Hall and Theodore Hänsch isone of more than 10 Nobels awarded (so far!) for laser-related research. This timelinemarking 50 years of the laser contains Physics World’s pick of events from laser history,including prizes (gold text), applications (green) and “firsts” (blue).A team led by Charles Townes builds the first “maser”, a forerunner of thelaser that had been described theoretically (and independently) byNikolay Basov, Alexander Prokhorov and Joseph Weber in 1952. Basov,Prokhorov and Townes share the 1964 Nobel Prize for Physics for their workon the “maser–laser principle”Gordon Gould coins the term “laser” in his lab notebook. The entry becomesthe basis of a 30-year patent disputeTheodore Maiman builds the first functioning laser, observing lasing actionin a crystal of pink ruby (16 May)William Bennett, Donald Herriott and Ali Javan invent the helium–neon gaslaser, the first to produce a continuous beam of laser light (12 December)Charles Campbell and Charles Koester perform the first laser surgery, destroyinga human patient’s retinal tumour using a ruby laserRobert Hall invents the semiconductor diode laserLasers are used to align a subway tunnel beneath San Francisco BayDennis Gabor wins the Nobel Prize for Physics for developing holographyThe first large-scale laser light shows are stagedMilitary laser target designators are used for the first time, during theVietnam WarFirst trials of laser supermarket bar-code scannersJohn Madey invents the free-electron laser195019531957196019611962196619701971197219741976

Image credits (top to bottom): American Institute of Physics/Science Photo Library; Emilio Segrè Visual Archives/American Institute of Physics/Science Photo Library; General Electric Research and Development Center, Emilio SThe first commercial laser-disc player, made by Philips, goes on sale.High costs mean the 12-inch disc format never really takes off. Philips hasbetter luck with the audio compact-disc player, which hits the market in 1982Nicolaas Bloembergen and Arthur Schawlow share the Nobel Prize for Physicsfor their “contribution to the development of laser spectroscopy”US President Ronald Reagan’s “Star Wars” speech reignites interest inweapons-related lasersSteve Chu, Claude Cohen-Tannoudji and William Phillips develop techniquesfor cooling and trapping atoms using laser light. The trio share the 1997Nobel Prize for PhysicsTAT-8, the first transatlantic fibre-optic cable, is completed, linkingNorth America and Europe. The first fibre-optic cable for inter-officecommunications had appeared 13 years earlier, when police in Dorset, UK,turned to Standard Telephones and Cables after a lightning strike knockedout their radio-transmitting equipmentSlow down! Lasers are used in the UK to inform drivers of excessive speedShuji Nakamura demonstrates the first blue laser diodeResearchers led by Wolfgang Ketterle create the first “atom laser” using aBose--Einstein condensate (BEC). In 2001 he shares the Nobel Prize forPhysics with Eric Cornell and Carl Wieman, who in 1995 had been the firstto observe a BEC in a dilute gas of atomsThe first laser “guide star” is used at the KeckII telescope in HawaiiBlu-ray discs introducedCharles Kao shares the Nobel Prize for Physics for his work on fibre opticsExperiments aimed at achieving “ignition” – the break-even point for nuclearfusion – begin at the US National Ignition Facility. The world’s largest laseris expected to reach this milestone within the next two years197819801981198319851988199019941996199720002002200620092010

The laser at 50: Boom, bust, boomphysicsworld.comThe bubble legacyThe technology crash of the early 2000s may have left many companies bruised, burned or broken,but several key advances in laser technology from that time are now bearing fruit, as Jeff Hecht explainsJeff Hecht is afreelance scienceand technology writerbased in Auburndale,Massachusetts,US, e-mail jeff@jeffhecht.com. He isauthor of the bookCity of Light, whichcovers the historyof fibre optics(2004 OxfordUniversity Press)Imagine an optics company – let’s call it JDS Uniphase– with a market capitalization approaching the grossdomestic product (GDP) of Ireland. Now imagine itmerging with a laser company – say, SDL – that hasa stock valuation of $41bn, higher than the GDP ofCosta Rica. Finally, imagine a start-up with $109m inventure capital in its pocket but no product to its name(Novalux) turning down an offer of $500m as insuf -ficient. It may be hard to believe, but these tales aretrue: they occurred in the year 2000 – an era when thelaser, fibre-optics and photonics industries were thedarlings of the financial world. Such was the madcapnature of that brief period that survivors call it simply“the bubble”.The bubble was born as the Internet took off in themid-1990s, pumped up by the explosive growth of theWorld Wide Web. Investors first noticed the “dot-comcompanies”, which were easy to caricature as a few peoplewith a website and a warehouse. But financiers’interest soon spread to other companies in the widertelecoms market, particularly firms making equipmentto build the “information superhighway”. By March2000, investors were eagerly pouring barrelfuls ofmoney into new optical technologies for a boomingtelecoms market.But the clock began ticking after the technologyheavyNASDAQ index of small-company stockspeaked above 5000 during one week in March 2000that saw investors mobbing that year’s Optical FiberCom munications Conference in Baltimore. First to fallwere the dot-com firms – the companies “selling dogfood on the Internet”, as chief analyst John Ryan frommarket-research firm RHK Inc. so eloquently put it.Businesses making communications hardware initiallyseemed less of a risk, but that did not stop the opticalindustry from also running off a cliff, where it hung suspendedin mid-air with its legs churning like the cartooncharacter Wile E Coyote – until it looked downand the law of gravity took hold. Start-ups crashed, withtheir remains sold on eBay for pennies on the dollar.Sales of the diode lasers used in telecoms dropped likeThe various laser-based technologiesthat emerged from the earlyInternet boom have become crucialboth within the telecoms industryand beyond36a stone (figure 1).In retrospect, it was an investment bubble as daftas the Dutch tulip bubble of the 17th century or theBritish South Sea bubble of the 18th century. Themoney largely evaporated as the bubble deflated. With -in a year, $1000 invested in Nortel stock had shrunk tojust $72. As one wry observer noted, investors wouldhave done better investing $1000 in Budweiser – thebeer, not the stock – and cashing in empty bottles at5 cents each. Today, JDS Uniphase is one of the luckycompanies still in business, with a market capitalizationof $2.5bn, about 2% of its peak value. It has dropped invalue by more than $100bn – more money than vanishedin the Madoff swindle – while Nortel has gone bust.But for every cloud there is a silver lining. The variouslaser-based technologies that emerged from theearly Internet boom have become crucial both withinthe telecoms industry and beyond.The quest for bandwidthThe dot-com bubble was built on the development offibre-optic cables, which became the backbone of theglobal telephone network in the 1980s. Such cables –essentially bundles of parallel glass fibres that carrylight – allowed more data to be sent over longer distancesthan was possible with previous microwaverelay towers or copper-cable systems. It was fibre-opticcables that carried the explosive growth of Internettraffic in the mid-1990s, which in turn created a hugedemand for yet higher transmission capacities. In about1999, Internet traffic was said to be doubling everythree months, although a later analysis by mathematicianand communications researcher Andrew Odlyzko,now at the Uni versity of Minnesota in the US, revealedthat this rate was achieved only briefly in 1995–1996.Still, the perception of a huge transmission demandfuelled heavy investment in new optical technologiesthat could provide the sought-after bandwidth.In fact, the two innovations that would prove centralto increasing fibre-optic bandwidth – namely, opticalfibreamplifiers and wavelength-division multiplexing(WDM) – were actually developed before the dot-comboom. The first of these innovations came as a responseto the problems with the fibre-optic cables of the 1980s,which could carry only one signal wavelength per fibreand needed “electro-optic repeaters” to be stationedroughly every 50 km to maintain signal strength. Theserepeaters converted an input optical signal into electricalform, before amplifying the signal and then turningit back into optical form – a cumbersome and costlyprocess. Optical-fibre amplifiers, in contrast, couldamplify an optical signal directly.Physics World May 2010

physicsworld.comThe laser at 50: Boom, bust, boomThe NASDAQ OMX Group, Inc.As for WDM, it allowed one fibre to simultaneouslytransmit many signals at different wavelengths, somethingthat had been impractical with electro-opticrepeaters. The idea of WDM had been around foryears, but had not been viable because the differentwavelengths had to be physically separated for am -plification at every electro-optic repeater. That allchanged in the mid-1980s when David Payne at theUniversity of Sout hampton in the UK invented theerbium-doped fibre amplifier – an optical fibre inwhich the silica light-guiding core has been dopedwith erbium atoms. Light from a “pump” laser directedalong the length of the fibre excites these erbium atomsto a state that naturally emits infrared light at a range ofwavelengths centred on 1550 nm when stimulated by aweak input signal. This multiplies the strength of anysignal transmitted over a band of wavelengths some25 nm wide – broad enough to allow signals at severaldifferent wavelengths to pass along the same fibre.Early erbium-doped fibre amplifiers were pumpedby large and expensive lasers, but soon smaller, cheaperPhysics World May 2010diode lasers were developed that could emit lightcentred on 980 nm and 1480 nm – the wavelengthsneeded to excite erbium. Meanwhile, new optical techniqueswere developed to divide the erbium-amplifierband into narrower segments, each containing a sep -arate signal. Initially, the signals were a few nanometresapart, but soon they could be separated by just 0.4 nm,thereby squeezing dozens of signals into a 25 nm band.By the mid-1990s, a rapidly growing army of research -ers working on these and other technologies had madeerbium-doped fibre amplifiers practical.Although slicing the erbium-amplifier spectrum intonarrower bands was good because it increased thenumber of slots available for transmitting WDM signals,it placed more demands on the diode lasers usedas transmitters. Initially, lasers were made that emittedprecise fixed wavelengths in the middles of thestandard WDM channels, which annoyingly meantthat a different diode laser had to be used for eachWDM channel. By 1998, however, tunable diode lasersap peared to be the answer and investors started flock-Money talksThe NASDAQ index ofsmall-companystocks peakedat 5079 in March2000, fuelled bydevelopments inlaser technology.37

The laser at 50: Boom, bust, boomphysicsworld.com1 Lasting legacy1086diode42non-diode01998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008100%79%50%27%25%15% 10%1% 2% 7%0%–36% –24% –50%Laser sales peaked at the height of the bubble in 2000, then dropped dramatically as thetelecoms market collapsed (upper graph). These year-by-year totals show that sales of thediode lasers used in telecoms are still less than two-thirds of their bubble-era peaks, whencarriers paid premium prices to build what turned out to be excess capacity. By the timedemand recovered and construction resumed, prices had come down. The lower graph showsthe year-on-year percentage rises or falls in total sales. Despite the fluctuations, the cumulativeannual growth rate over the period shown was 7%.$ (billion)38ing to the companies developing them. As the bubblegrew, investors even chased half-baked ideas such as“all-optical networking”, which envisioned redirectingthe signals by changing their wavelength, but thoseschemes came to naught.Telecoms technologyThe telecoms bubble eventually collapsed because themarket had wildly overestimated the demand for telecomscapacity. Investors had funded too many companiesdoing similar things, while network operatorssuch as AT&T and Verizon had installed far more fibrethan they needed, and it took years for demand tocatch up. Yet the crucial technology – laser transmitters,fibre amplifiers and “closely packed” WDMoptics that could cram in dozens of different wavelengthsinto a single fibre – worked fine. Recent yearshave even seen data rates start to climb again. The firststep was to 40 Gbits s –1 per wavelength and in De cem -ber 2009 Verizon switched on a system transmitting at100 Gbit s –1 on a single wavelength between Paris andFrankfurt – enough capacity to send 2.5 fully packedsingle-sided DVDs in a single second.Tunable diode lasers have been another major winner.They have largely replaced fixed-wavelengthdiode lasers in WDM systems because they are onesize-fits-allcomponents. When a system is installed,software adjusts the lasers so that they emit at the de -sired wavelengths, then locks them in place. Althoughsome tunable lasers are used in subsystems where theirwavelengths may be changed when the network configurationis altered, most tunable lasers are set to onewavelength and left there. “It’s sort of a dull use of tunability,”says optoelectronics engin eer Larry Coldrenof the University of California, Santa Barbara. It doesthough fulfil system requirements.Laser Focus WorldColdren has personal experience of the telecomsbubble, having founded a company in 1998 calledAgility Com munications to produce tunable diodelasers in which the wavelength of the light emitted isselected by slightly expanding or contracting the multilayeredreflective structures that make up the diode.“Agility was worth a lot of money before it [even] hada product or a customer,” says Coldren, who had in -vented the diode-tuning technique a decade earlier.Investors poured more than $200m into the firm andColdren stayed with the company until it was boughtby JDS Uniphase in 2005 for $67m in stock and cash –a third of the money it had burned through.Although it took years to make tunable diode lasers asgood as fixed-wavelength diodes and to package themwith control electronics for system use, sales did, however,eventually begin to rise once the packaged tunablelasers beat the price and performance of fixed-wavelengthlasers. Indeed, Coldren is sure that such tu nablelasers will be around for years to come. “We even usethem here at the university because they’re robust, easyto make and very forgiving,” he says. Their design in -herently yields a single frequency – all it takes is tu ningand calibration to obtain a desired wavelength. Evenfirst-year graduate students can do it, Coldren explains.Pumped by successAnother bubble-era technology that has proved a hitbeyond the telecoms sector is the high-power diodelasers that were originally designed to pump fibre am -plifiers. These lasers have since been adapted to pumpa growing variety of solid-state lasers, which previouslyhad been pumped by bright lamps. This process wasinefficient because much of the lamp energy was emittedat wavelengths not ab sorbed by the laser material.Laser pumping is, in principle, much better because thelaser can be fabricated to emit only light matching theabsorption lines of chosen solid-state materials.Although early diode lasers could convert a largerfraction of input power into pump light than was poss -ible with lamps, they still only emitted milliwatts ofpower. Undeterred, military agencies took a keeninterest in developing more powerful pump diodes inthe 1980s and 1990s, realizing that such devices couldbe used to pump lasers that mark targets for smartbombs, or perhaps for laser weapons. But during thedot-com bubble, when building pump diodes for fibreamplifiers appeared more lucrative, companies likeSDL started switching their attention from the defenceto the telecoms market.That meant moving away from the 808 nm gallium–arsenide pump diodes sought for military applicationsand focusing instead on a new family of indium–gallium–arsenide (InGaAs) devices that emit in the980 nm erbium pump band, as well as indium– gallium–arsenide–phosphide (InGaAsP) devices emitting at the1480 nm erbium pump band. That new focus was onereason why SDL – the biggest manufacturer of pumpdiodes – was worth a staggering $41bn when JDS Uni -phase an nounced plans to buy it in July 2000.Market valuations have declined since those headydays, but pump-diode technology has boomed, andnot only in fibre amplifiers for telecoms. Pump diodesare displacing the pump lamps long used to powerPhysics World May 2010

physicsworld.comThe laser at 50: Boom, bust, boomneodymium-doped solid-state lasers, while today’sgreen laser pointers are miniaturized frequency-doubledneodymium lasers, pumped by battery-powereddiode lasers. (They are not strictly green lasers as theydo not generate green light; instead, they take infraredlight and double its frequency using nonlinear crystalsso that it emerges as green.) At the opposite end of thepower scale, the US defence firms Northrop Grummanand Textron Systems have each demonstrated 100 kWsolid-state laser weapons pumped by diode lasers.These much more powerful lasers – which could beused to track, illuminate and then ignite enemy rockets,artillery and mortars up to a couple of kilometresaway – are much smaller and easier to use than theywould be without pump diodes.Variations on a themeDiode pumping has also been the key to success for avariation on another bubble-era technology: a noveltype of semiconductor laser called the vertical-external-cavitysurface-emitting laser (VECSEL) that hadoriginally been developed by researchers at the Massa -chusetts Institute of Technology’s Lincoln La bor atory.The laser light in a VECSEL emerges from the top ofa wafer, not from the edge as in usual diode lasers, andthe device contains one external mirror and one at thebottom of the chip.During the bubble, Aram Mooradian – a Lincoln Labalumnus – landed over $100m in venture capital toset up a company called Novalux to build electricallypumped VECSELs for telecoms. That market nevergot off the ground, and, after burning through $193m inventure capital, the firm was finally sold in 2008 for amere $7m to Arasor International, an Australian startup.Its shares were last seen selling for 2 cents each.However, diode-pumped VECSELs – also knownas optically pumped semiconductor lasers – are doingmuch better, having become a hot new approach tomaking visible solid-state lasers (figure 2). The big ad -vantage of optically pumping a semiconductor laser inthis way is that the laser can generate wavelengths itcannot produce if it is pumped electrically. One leaderin the field is the US firm Coherent, which has used thisapproach to generate watt-range powers at, for ex -ample, an infra red wavelength of 1154 nm that can bedoubled in frequency in a nonlinear crystal to create ayellow 577 nm beam. This wavelength is important intreating diabetic retinopathy, a common cause of blindnessarising from the spread of abnormal blood vesselsacross the retina. When the laser illuminates the retina,oxygenated haemoglobin in the blood vessels absorbsits emission, heating and destroying the vessels.The power of fibreBut easily the most successful bubble-era spin-off arefibre lasers, which now deliver kilowatt-class powersfor industrial applications and ultrashort pulses forresearch. Like fibre amplifiers, fibre lasers use rareearth-dopedfibres pumped from their ends by diodelasers. The rare-earth metal is confined in a small innercore with high refractive index, which is surrounded byan outer core made of lower-index glass that confineslight from the pump diodes. The dual-core structurepasses the pump light repeatedly through the innerPhysics World May 20102 Spin-off successactive region Bragg mirrorsubstratequantum wellsoutputcouplerOne successful technology from the telecoms bubble of the early 2000s is a novel type ofoptically pumped semiconductor laser known as the vertical-external-cavity surface-emittinglaser (VECSEL). At the heart of these devices (left) is a series of sandwich-like layers ofsemiconducting material – known as quantum wells – sitting on top of an internal “Bragg”mirror that is deposited in turn on a substrate such as the “III–V” semiconductor galliumarsenide. As shown on the right, the light emerges from the top of the device, not from the edgeas in usual diode lasers. The VECSEL is pumped by light from a semiconductor diode laser,while a “heat sink” – a metal block or slab – conducts heat generated from the VECSEL awayand it is cooled either by flowing water or simply air convection. The “output coupler” is a mirrorthat transmits some light and reflects the rest back into the laser cavity to produce oscillation,while the “intercavity elements” are one or more optical devices that in this case double thefrequency of light generated in the VECSEL.core, so that most of the pump energy is converted intolaser output. With the best materials, the conversionefficiency can reach 80% in the lab – impressively highby laser standards. Another benefit of this fibre geometryis a large surface-area to volume ratio, easing theremoval of waste heat, which has been a problem withbulk rod or slab solid-state lasers.Bubble-era developers looked at many rare-earthdopants for optical fibres. Ytterbium is the most at -tract ive for high-power operation because it can bediode pumped using light at wavelengths only slightlyshorter than the output wavelength, which means thatthe emitted photons can contain more than 90% of thepump-photon energy. (The total pump efficiency is,however, limited to no more than 80% because not allof the excited atoms emit laser photons.) Ytterbiumemits light at wavelengths of about 1030 nm, close tothe 1064 nm emission of neodymium, which means thatytterbium-fibre lasers with higher power and efficiencycould replace widely used neodymium solid-state lasersfor many applications.Fibre lasers can reach impressive power levels. IPGPhotonics, for example, has built fibre oscillator amplifierswith single-mode powers of 10 kW and multimodepowers, with much lower beam quality, of 50 kW. Thoseare among the highest powers available from any commerciallaser. Although some of its lasers are so power -ful that military agencies have field-tested them for thedestruction of improvized explosive devices and un -exploded ordnance on the battlefield, IPG’s main businessis selling lasers that can be used in industry forapplications such as cutting metals (figure 3). Fibreslaser cavityintracavityelementssemiconductor-diodepump laserheatsinksemiconductordiskpump optics39John-Mark Hopkins, University of Strathclyde

The Little Bookof String TheorySteven S. Gubser“This is an engaging and conciseintroduction to the main ideas in stringtheory. Gubser gives us a quick tour ofthe basic laws of physics as we understandthem today, and then demonstrates howstring theory seeks to go beyond them.He serves as an artful and attentiveguide, as the reader explores the mysteriesof quantum mechanics, black holes,strings, branes, supersymmetry, and extradimensions in the pages of this book.”—Juan Maldacena, Institute forAdvanced StudyScience EssentialsCloth $19.95 £13.95 978-0-691-14289-03 At the cutting edgephysicsworld.comIPG Photonics40Physics and Technologyfor Future PresidentsAn Introduction to the EssentialPhysics Every World Leader Needsto KnowRichard A. Muller“Muller has distilled the most importantscientific principles that define ourchoices, and has presented them clearlyand objectively. To make wise decisions,not only future presidents, but futurebusiness and community leaders, andthoughtful citizens generally, need theinformation in this book.”—Frank Wilczek, Nobel Prize–winningphysicistCloth $49.50 £34.95 978-0-691-13504-5High Energy Radiationfrom Black HolesGamma Rays, Cosmic Rays,and NeutrinosCharles D. Dermer& Govind Menon“Filling an important gap in a topicaland fast-evolving area, this interestingbook will be a valuable addition to theastrophysics literature. The scientificcontent is of a high quality, and includesa notable level of rigor in the derivations.”—Peter Mészáros, PennsylvaniaState UniversityPrinceton Series in AstrophysicsDavid N. Spergel, Series EditorPaper $75.00 £52.00 978-0-691-14408-5Cloth $120.00 £82.50 978-0-691-13795-7(0800) 243407 UK800.777.4726 USpress.princeton.eduSparks fly as an ytterbium-doped fibre laser cuts a thick sheet of metal.deliver the beam as well as generate it – an approachthat makes the systems rugged and reliable, which iscrucial for industrial applications.The high efficiency and ease of heat dissipation allowfibre lasers to be small, and coupling fibres togetheravoids the need for complex beam-delivery optical systems,making them simple and convenient for researchapplications as well as industry. Erbium-doped fibrelasers can generate pulses lasting just a few femtoseconds(10 –15 s), as well as frequency combs, which gen -erate uniformly spaced lines across the visible andnear-infrared spectrum. There have even been propo -sals to use them on spacecraft for precision-measurementapplications. Fibre lasers have also demonstratedsome impressive research feats. Last year, for example,Al fred Leitenstorfer at the Univer sity of Konstanz inGer many used a fibre laser to generate the first singlecyclepulses – pulses that are literally so short that theycontain just one oscillation of light.Boom, bust, boomTechnology industries are notorious for their boom/bust cycles. The railroads went through them in the19th century, as did lasers in the late 1960s and early1970s. The telecoms bubble that peaked in 2000 wasunusual only in how badly it overinflated values, andhow hard it crashed. Survivors woke up the morningafter with a dreadful hangover, and swore they wouldnever binge again. But I suspect that if a new round offinanciers arrived with bucketfuls of money, the survivorswould go for it again, vowing that this time theywould take the money and run before it was too late.One thing is for sure, however: the global fibre-opticnetwork that under pins the 21st-century informationbasedeconomy has revolutionized the world – and willcontinue to do so for many years to come.Physics World May 2010

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physicsworld.comThe laser at 50: The green gapPatrick Landmann/Science Photo LibraryGoing for greenWith manufacturers keen to start selling us mobile phones that can project TV pictures onto any nearbysurface, a race is on to develop tiny diode lasers that can emit green light. Andy Extance reveals thechallenges involved in bridging the green gapThousands of times per second a point of light turnson and off, moving side to side, top to bottom. It is arhythm that ticks around the world, illuminating livingrooms and office desks in the process. However, thecathode-ray TVs and monitors that metronomicallyfire electron guns at viewers – who are shielded onlyby thin sheets of glass – are rapidly being replaced byflat-screen technologies. Yet as the creation of imagesusing scanning electron beams fades into history, a newform of technology is emerging that builds up picturesby scanning with light.“One target is that everyone has the chance to sharevisual information at any time, in any location,” saysUwe Strauß, director of semiconductor lasers at Ger -many’s Osram Opto Semiconductors. The firm is tryingto create green diode lasers suitable for use in “flyingspot” projectors. These devices use a mirror to combinered, blue and green laser light into a single beam, whichscans back and forth rapidly. The light creates an image,pixel by pixel, that remains in focus regardless of the distanceto the surface onto which it is shone.To fabricate green laser diodes – millimetre-sizedsemiconductor chips containing all the necessary componentsto emit laser light – the Osram team and itsrivals must first tackle nanometre-scale defects andcomplex electronic phenomena in the materials thatPhysics World May 2010they need to use. Their motivation for undertaking thisquest? The rewards available from enabling projectorsthat can penetrate the billion-unit-a-year mobile-phonemarket. If they succeed, we could soon be using gadgetsadded to our phones – just like digital cameras havebeen – to watch TV projected onto any nearby surface,from the convenience of wherever we happen to be.Double troubleThe tiny semiconductor diode laser is familiar to usfrom its use in CD and DVD players, and the more re -cent excursion into Blu-ray. But while lasers in thesedevices can generate light at infrared, red and bluevioletwavelengths, respectively, there are still no greendiode lasers widely available for the commercialmarket. While green diode lasers do exist in researchlabs, they are only just crossing into the green spectrumfrom the blue, and with tiny power outputs of only a fewmilliwatts, they are not useful commercially (figure 1).However, do not get the impression that green laserlight cannot be created or that it is not currently usedfor practical purposes: it can be made by using large andexpensive gas lasers or by firing red light at special“frequency doubling” crystals. These lasers are used inmedicine, for example, because green laser light canpenetrate human tissue only to a very shallow depth. ItAndy Extance isa science writerbased in the UK,e-mail aextance@supanet.com43

The laser at 50: The green gapphysicsworld.com1 The green gapmaximum output power (mW)1000100101380 420 460 500 540 580 620 660 700lasing wavelength (nm)Various colours of visible light have been achieved with laser diodes, but there is a gaping holeat green wavelengths. Scientists are trying to solve the problem by tweaking their designs ofblue laser diodes (based on gallium nitride and indium gallium nitride), but as greenerwavelengths are reached, the output power falls dramatically – below the 50 mW that devicemanufacturers are demanding. On the other side of the gap, researchers are not going for greenbut instead for high power in their red laser diodes (made from aluminium indium galliumphosphide), which explains the steep vertical drop-off on this side. This graph shows publisheddata for laser diodes up to March this year.Portable projectionProjectors forinclusion in mobilephones are drivingthe development ofgreen diode lasers.44Microvision Inc.can be used to precisely vaporize swol len prostate-glandblockages stopping urine flow in men and to reduce thepain felt by patients being treated for retinal damage.These lasers, however, would be im practical for use inmobile phones.The problem is that even miniaturized frequencydoublinglasers are both bulky and power-hungry incomparison with laser diodes. The extra componentsneeded – a semiconductor laser that takes light froman 808 nm laser diode and converts it to 1060 nm,before a crystal halves this wavelength to 530 nm greenlight – make the overall device relatively bulky at about400 mm 3 . Red and blue diode lasers, in comparison,are about 30 mm 3 in size. “It would be nice to have agreen laser at this small size,” says Strauß. Althoughthe small green lasers used in laser pointers and insome of the projectors found mounted in lecturetheatres are frequency-doubled lasers, they woulddrain battery power from phones too quickly to be -come the world-conquering display technology thatOsram envisions. “If you want to watch a show on yourmobile phone, you need to be able to project for atleast one hour,” ex plains Strauß. “This means youneed to control power consumption.”Problematic materialsThe wavelength of light that a laser diode emits is inpart a fundamental property of the semiconductor crystalfrom which the diode is made. It is determined bythe separation between the conduction and valenceenergy bands that electrons in a semiconductor caninhabit. The diode design injects electrons from theS Nakamura and H Ohta, University of California, Santa Barbarahigher-energy conduction band and positively chargedholes from the valence band into an area of the deviceknown as the quantum well. As the electrons then fallinto the valence band, they recombine with the holesand light is emitted at a wavelength corresponding tothe energy difference between the two bands. Highlyreflective surfaces surrounding the quantum well forma laser cavity, trapping the light, which stimulates moreelectrons and holes to recombine, thus amplifying theemission. Light typically exits such devices at the edgesof the quantum well.Gallium arsenide phosphide (GaAsP) was the firstlight-emitting semiconductor to prove commerciallysuccessful, initially in red light-emitting diodes displayingnumbers on calculators and wristwatches in the1960s. From the mid-1970s onwards the same materialwas used in the development of laser diodes for opticalnetworking and CD players. The emitted wave lengthcan be altered by changing the proportions of arsenicand phosphorus, which in turn alters the semiconductor’sband gap. When the ratio of arsenic to phos phorusis 65:35, the band gap is about 1.97 eV, emitting 630 nmred light.To make working lasers, manufacturers must limitthe number of a type of defect known as a dislocation inthe semiconductor crystal, because electrons and holescan recombine at these defects without emitting light.For lasers based on GaAsP, there is a critical limit ofabout 10 000 dislocations per square centimetre, abovewhich insufficient light is produced to allow lasing.Almost 50 years of research has ensured that defect levelsof below this are routinely achieved in to day’s redand infrared laser diodes, allowing low-cost devices tobe produced.After the development of GaAsP devices, researchinto other visible wavelengths largely focused on semiconductorssuch as zinc selenide to try to achieve blueand green light. In the 1990s these were overtaken byblue light emitters made from gallium nitride (GaN),which had previously been overlooked by many re -searchers as it was difficult to produce with good crystalquality. That was until Shuji Nakamura, then ofJapanese light-emitting diode and laser-diode makerNichia, and now of the University of California, SantaBarbara (UCSB), discovered that it could perform welleven with 10 000 times more dislocations than GaAsP.GaN’s 3.4 eV band gap can nearly produce the 405 nmviolet emission used for Blu-ray players without furtheralteration. However, to get a band gap correspondingto longer “true blue” wavelengths of about 450 nmrequires added indium, while green wavelengths abovethe 510 nm minimum needed for projectors require stillhigher indium contents. Unfortunately, when there istoo much indium, the large number of dislocations be -comes a real problem.Laser diodes are produced using crystal-growthtechniques collectively known as epitaxy, in whichmaterials are fabricated atomic layer by atomic layer,typically at high temperatures and under vacuum conditions.The GaN is grown on thin circular wafersknown as substrates, which are sliced from a largercylindrical crystal “boule”. Including indium degradesthe quality of the material, so balancing the amount ofindium (to get longer wavelengths) with the crystalPhysics World May 2010

physicsworld.comThe laser at 50: The green gapquality (affecting lasing ability) is a challenge. “Theproblem is that indium is grown at a lower temperaturethan gallium nitride,” Strauß explains. “Low temperaturemeans low crystal quality.”Poles apartAnother key challenge arises from a different fundamentalproperty of indium gallium nitride, namely thatthe electrons and holes in the material can be unevenlydistributed. The resulting imbalance in electroniccharge creates an electric field known as a polariza -tion field. When GaN laser diodes are deposited onstandard substrates, a polarization field runs throughthe device in the direction perpendicular to the surface.The field is created by an excess of electrons onthe top surface of the device and a deficit on the bottom.The interaction of the polarization field with thematerial on a quantum-mechanical level – known asthe Stark effect – narrows the band gap, which is usefulas it pushes the wavelength of the light emitted furthertowards green. However, the field also comes withdrawbacks. It makes it harder for electrons and holesto meet in the quantum wells of both laser diodes andlight-emitting diodes. Instead, the electrons and holesare more likely to recombine and re lease energy asheat. “That’s wasted charge,” says Jim Speck, a ma -terials scientist at UCSB. Another difficulty is thatwhen current flows through the laser, it creates an electromagneticfield that screens the electrons in thequantum well from the polarization field, widening theband gap again and shifting the emitted light backtowards blue.UCSB researchers were among the first to show thatchanging the crystal direction along which GaN substratesare sliced – and so modifying the direction ofthe polarization field in diodes grown on them –improves laser-diode performance (figure 2). Cuttingwafers vertically rather than horizontally from theboule means that diodes fabricated on them have thedirection of the polarization field similarly rotated by90°. The substrates are therefore called “non-polar” as,oriented in this direction, the polarization field nolonger influences the vertical movement of electronsand holes towards each other. “Semi-polar” substratesare cut somewhere in between, where the effect of thepolarization field is still there to some extent. “The bigbreakthrough for us came in late 2006 when we wereable to get high-quality non-polar and semi-polar substrates,”explains Speck. Using non-polar substrates,Speck and co-workers were able to achieve a wavelengthof 492 nm – almost, but not quite, green.But researchers have differing opinions about whichcut is best. Strauß, for example, is not convinced thatnon-polar substrates are definitely the best way to producegreen lasers. “I don’t know whether the polar -ization field is really the major problem,” he says. “It’smore than 50% a question of material quality.” Heexplains that because non-polar substrates lose theband-gap-narrowing effect of polarization, the amountof indium used must be increased further, making thecrystals harder to grow. Rather than increasing theindium content quite so much to achieve green wavelengths,Strauß says that keeping quantum wells thinmakes it possible to minimize the electromagneticPhysics World May 20102 Plane as dayNGanon-polarThe wavelength of light emitted by laser diodes grown on gallium nitride (GaN) surfaces isinfluenced by the orientation of the crystal they are made on. The GaN unit cell (left) can be cutalong different crystal planes (right) to affect the direction of an ever-present polarization fieldrunning through the laser diode. Diodes grown on a polar surface have this field runningvertically through the device. This narrows the band gap, thus allowing green emission at lowcurrents, although at higher currents the polarization field is masked, widening the band gapand moving emission into bluer wavelengths. Diodes grown on non-polar surfaces do not sufferfrom this variation. However, without the polarization field, higher proportions of the galliummust be replaced with indium to achieve the correct band gap to produce green light. This isalso a challenge as it is difficult to make working laser diodes with high indium contents.Semi-polar surfaces, cut at angles between vertical and horizontal, present a compromise, withsome also able to accommodate particularly high indium contents.non-polarscreening caused by current flow that can push greenlasers back into the blue seen in conventional substrates.Using this ap proach, Stephan Lutgen, Osram’shead of nitride-laser development, was able to present50 mW output 515 nm lasers at the Photonics West conferencein San Fran cis co in February this year.It is not known why, but slicing the GaN boule in differentdirections can also help to increase its indiumcontent. Substrates produced from a plane inclined at58° from the conventional orientation allow the highestindium content of all orientations, Speck says.These substrates are semi-polar, but here the polar -iza tion field brings the electrons and holes together,rather than separating them. “The electric field isworking with the diode,” Speck explains. “The physicsis more favourable.”Another research group exploiting an unusual crystalorientation with advantageous polarization isat the Japanese firm Sumitomo Electric. In 2009 itsre search ers took the lead in the race for green, bydemonstrating 520 nm lasers. However, that title hasnow been reclaimed by a spin-out company establishedby Speck, Nakamura and fellow UCSB re -searcher Steven DenBaars called Kaai, which is setto move into production with its non-polar/semi-polarapproach. Kaai reported a 9 mW continuous-wave523 nm laser at this year’s Photonics West conference.Regardless of these achievements, Strauß points outthat projector makers need green laser diodes withpower outputs of at least 50 mW. While Kaai aims todemonstrate this at wavelengths above 520 nm laterthis year, Strauß notes that this does not mean that thedevices will be widely available immediately thereafter.“To get high yields and to get stable high-volume productionso that the customer is satisfied will take someadditional time,” he says. “The race is open, and we donot know which laser will be the first, or which will bethe best.”polarProjectormakers needgreen laserdiodes withpower outputsof at least50 mW45

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physicsworld.comThe laser at 50: Attosecond lasers and beyondBeyond ultrafastAs pulsed lasers are developed to resolve dynamics occurring on ever smaller time and length scales,Adrian Cavalieri reviews the laser technology that has enabled us to directly observe incredibly fastprocesses, in fields ranging from atomic physics to molecular biologyThorsten Naeser, Max Planck Institute of Quantum OpticsSince the first days of the ruby laser 50 years ago, lasersystems have steadily improved thanks to advances inlaser gain media and mirror technology. On the onehand, incredibly powerful lasers have been developedfor fusion research that are able to deliver huge pulsesof energy to their targets, resulting in local environmentssimilar to the interior of the Sun; on the other,we now have lasers that can precisely deliver ultrashortpulses of energy to atomic, molecular and condensedmattersystems to trigger various physical processes andto measure their instantaneous characteristics.The term “ultrafast” was originally coined in 1982 todescribe dynamical processes observed with lasers thatPhysics World May 2010occur on the sub-picosecond (10 –12 s) or femto second(10 –15 s) timescale. However, the phrase has now be -come essentially outdated, as processes on the attosecond(10 –18 s or 1 as) timescale – 1000 times shorter thana fem tosecond – are now accessible (see box on page51). Indeed, attosecond spectroscopy could lead to theability to directly observe charge transfer in photovoltaiccells and transistors, for example, allowingresearchers to understand precisely how the electronsmove around such devices. This knowledge could helpus to create photovoltaic cells that are more efficient,and transistors that switch faster, both of which wouldimpact on our daily lives.Adrian Cavalieri is aprofessor of physicsat the University ofHamburg, Germany,and head of aresearch group at theMax Planck ResearchDepartment forStructural Dynamicswithin the Center forFree-Electron LaserScience, e-mailadrian.cavalieri@mpsd.cfel.de47

The laser at 50: Attosecond lasers and beyondphysicsworld.com1 Four-level picturelevel 4pumpphotondecayupper lasing state (level 3)low-frequency,long-wavelength photonhigh-frequency,short-wavelength photonlower lasing state (level 2)decayground state(level 1)The lasing media used for pulsed lasers allow lasing transitions with a large range of energies,which thus emit photons with a large range of frequencies. Here, the laser gain material – adoped crystal – is “pumped” by photons from an excitation source, such as a very bright whiteflashed lamp or another laser, specifically tuned to the pump transition energy. Absorbed“pump” photons transfer their energy to electrons in the ground state (level 1), exciting them to ahigher energy (level 4). Next, through a decay process such as a vibration, the electrons relaxinto the upper lasing state (level 3). When the electron population in level 3 is greater than thatin level 2, the lower lasing state, a “population inversion” is said to exist and the conditions areset for stimulated emission. When an electron decays from level 3 to level 2, a photon isemitted, which, if a population inversion exists, can “stimulate” another electron in level 3 todecay to level 2, emitting a second photon, and so on. The stimulated photons are emitted in thesame direction and in phase with the first, resulting in the emission of coherent laser radiation.48Pump it upWhile some lasers operate in a continuous-wave mode,emitting radiation with nearly a single monochromaticfrequency, pulsed lasers emit radiation over a broadrange of frequencies – billions in fact. These frequencycomponents are timed exactly so that their electric fieldsnearly cancel each other out, except for during one tinyperiod of time when they combine constructively in oneintense pulse. So when we refer to a pulsed laser, thereis no mechanical shutter controlling when the light isemitted; rather, the pulse is created by coherent radi -ation with many different frequencies interfering.The frequencies of light that exist in a laser’s res onantcavity are determined by two factors. First, they dependon the lasing transitions that occur in the laser gainmedium. In pulsed lasers, a gain material is chosen thathas many different lasing transitions (figure 1). Second,the cavity dimensions only allow light frequencies forwhich the electric field has nodes at the cavity’s endmirrors. With the right material and cavity it is possiblefor billions of frequencies to lase simultaneouslyand generate a short pulse (figure 2).Because they alternate between a short burst of emissionknown as the “pulse” and a much longer downtimein between, pulsed lasers can produce high peakpowers: since power is energy per unit time, compres -sing a fixed amount of energy into a shorter time intervalresults in a higher peak power. Using the 10 3 –10 4 Wof power from a standard wall socket, for example,lasers can easily produce pulses with terawatt (10 12 W)peak powers – but only for a few millionths of a billionthof a second.As in stroboscopic photography, where the fastestmotion that can be captured is defined by the camerashutter speed or the duration of the flash, ultrafasttime-resolved studies on the femtosecond and nowattosecond timescale are generally bound by the durationof the laser pulse. In ultrafast, time-resolved“pump–probe” experiments, a first pulse, called the“pump pulse”, is used to trigger a dynamic process,while a second subsequent pulse, called the “probepulse”, is used to observe the system a short period oftime later. Today, we can access the attosecond regime,with the production of laser pulses as short as 80 as.Hand in hand with pulsed lasers is the field of nonlinearoptics. Typically, when light passes through atransparent material, the polarization of the material– the distribution of positive ions and electrons – isaffected proportionally (or almost) to the intensity ofthe incident light, i.e. the optics are linear. However,any deviation from a truly proportional response re -sults in nonlinear effects that can become significant ifthe light propagates through a very thick material orthrough a long fibre-optic cable, for example. Butrather than using low-intensity light and very thick orlong materials, nonlinear effects can also be studiedusing thinner materials and a very intense, coherentlaser beam. Thus the field of nonlinear optics beganshortly after the invention of the laser in 1960.Indeed, only a year later, researchers at the Universityof Michigan showed that laser light could be doubled infrequency when fired into a normally transparent quartzcrystal. Since then, we have taken advantage of ourunderstanding of this “second-harmonic generation”,and other nonlinear pro cesses, and fed-back the know -ledge into the design of pulsed lasers. Coming full circle,nonlinear effects are now inherent in nearly everystep of creating a laser pulse, and present a promisingroute to the next generation of laser technology.Sapphire to startOne of the first steps towards attosecond pulsed lasersoccurred in 1981 with the demonstration of titaniumdopedsapphire, or Ti:sapphire, as a suitable broadbandlaser gain crystal by Peter Moulton at the Massa chusettsInstitute of Technology. Ti:sapphire is unique in thatwhen it is pumped by a continuous-wave laser, a hugerange of lasing transitions can occur. While the laserthat pumps the Ti:sapphire is narrowband, i.e. nearlymonochromatic, Ti:sapphire emits over a range of frequenciesand is broadband. From Heisenberg’s energy–time uncertainly principle, ΔEΔt ≥ h – /2, a broad bandwidthof laser energies, or frequencies, is required toproduce a short pulse of laser light: the greater thebandwidth, the shorter the pulse.Pumped by a laser with a wavelength of approximately530 nm, Ti:sapphire emits light with wavelengthsfrom about 600–900 nm (orange to infrared).But while a broad range of colours, or frequencies, areproduced, a pulse is not created without some furtherintervention. What is needed is for the laser frequenciesto be in phase at some point in the cavity.Forcing the various frequencies into phase isachieved through a process known as “mode locking”.The laser pulse then exists at the dynamic point in spaceat which the many frequencies are in phase with eachother. This “point of coincidence” moves back andforth in the cavity at the speed of light, as the phasePhysics World May 2010

physicsworld.comThe laser at 50: Attosecond lasers and beyond2 Constructive interference3 Near-single-cycle optical pulseelectric field (arbitrary units)electric field (arbitrary units)–20 –15 –10 –5 0 5 10 15 20time (fs)Frequencies that are in phase sum to produce a pulse. The bottomcurve (red) is a sum over the four representative curves shown in blue,as well as about 500 others with frequencies in between. Thetop-most blue sine wave shows the highest frequency component andthe bottom-most wave shows the lowest. The electric fields of thedifferent light beams are in phase and interfere constructively at onemoment in time, before falling off quickly and just about cancellingout until the next in-phase moment a relatively long time later.velocity and group velocity of light are nearly identicalin air. Each time the pulse passes the “output coupler”where the laser light leaves the cavity, which can bethought of as an imperfect mirror, a portion of the pulseis emitted. The emitted light appears as pulses sep -arated by the cavity round-trip time. Today’s mostadvanced Ti:sapphire oscillators emit optical pulseslasting about 5 fs – barely a few cycles of the electricfield and near the fundamental limit. Maxwell’s equationsof electrodynamics tell us that the shortest pulseof light that can ever be generated is equal to a singlecycle of the carrier electric field (figure 3).Chirping and harmonyTo generate shorter, attosecond pulses, the laser lightmust be shifted to shorter wavelengths. But before thisconversion can be achieved, the pulses need to bemuch more energetic and so are amplified in energyfrom several nanojoules to the millijoule level. So asnot to damage the crystal used to amplify the energy,“chirped-pulse amplification” – first de monstrated byGerard Mourou at the University of Rochester in 1985– is employed, where the pulses are stretched in timeto as long as a nanosecond by “de-phasing” their frequencycomponents to reduce the peak intensity ofthe pulse. Fol lowing amplification, the pulses arerecompressed in time by putting the frequency componentsback in phase. Next, the amplified pulse isshortened using a spectral broadening and pulse-timecompression stage, which uses nonlinear effects ina noble gas and dispersive mirrors that correct foradditional de-phasing in the broadening process. Cur -rently, the most advanced Ti:sapphire amplifier systemsutilizing all of these components can produceoptical pulses as short as 3.3 fs with up to half a millijouleof energy. So now we have laser pulses that havemuch more energy than when we started but are stillPhysics World May 2010–10–8–6–4–2 0 2time (fs)6 8 10This figure shows a simulated near-single-cycle laser pulse, which isnearly the shortest optical pulse that can be generated. The “drivepulse” envelope (black) simply characterizes the pulse and is anartificial construct. The light’s carrier electric field (red) drivesphysical phenomena. The real pulse results from constructiveinterference of a broad band of frequency components. This opticalpulse needs to be converted to extreme-ultraviolet radiation to createan attosecond pulse.not yet in the attosecond regime.Because light pulses cannot be shorter than one oscillationof the carrier electric field, or the light’s wavelength,the shortest pulse that Ti:sapphire could emitfor light pulses centred on 750 nm, or near-infrared(NIR), is 2.5 fs. Evidently, attosecond laser pulses mustbe composed of shorter wavelengths, equivalent tousing photons with higher energies. For pulses shorterthan 100 as, this requires the light to be in the extremeultraviolet (XUV) range, where typical photons havea wavelength and energy of about 12 nm and 100 eV,respect ively. Converting the Ti:sapphire NIR photons(at about 1.6 eV) to XUV photons (at 100 eV) requiresa significant energy boost. The NIR pulses are convertedinto attosecond XUV pulses through a processknown as “high-order harmonic generation” (HHG)(figure 4). Today, using this method, the shortest pulsesare 80 as in duration.There can be up to 10 8 photons in the attosecondpulse; but while this sounds like a lot, it is not enoughto be split into the two pulses required for standardpump– probe experiments and also obtain a goodenough signal-to-noise ratio to measure anything. Ifthere were enough photons to do such experiments,the time resolution would be limited only by the atto -second pulse duration, as is the case in more standardToday’s most advanced Ti:sapphireoscillators emit optical pulseslasting about five femtoseconds –barely a few cycles of the electricfield and near the fundamental limit449

The laser at 50: Attosecond lasers and beyondphysicsworld.com4 From infrared to extreme ultraviolet1000XUV filterpotential energy0potential energy0intensity (counts)0radial co-ordinate0radial co-ordinateCreating attosecond pulses requires a process known as “high-order harmonic generation”, in which near-infrared laser pulses are shone into aninert gas jet. The electrons in the gas atoms, originally in an unperturbed atomic well (dotted black line), see a different potential (red) when thelaser electric field (solid black line) perturbs the potential. What happens is that the laser electric field folds down the potential of the atomic well(left), increasing the probability that an electron will escape by tunnelling through the barrier and be accelerated away from its parent ion by thesame electric field. When the oscillating electric field changes its sign (which happens every half-cycle), the electron’s direction of travel isreversed and it is accelerated back towards its parent atom. The electron then recombines with its parent atom (middle) and releases the kineticenergy that it gained while being accelerated in the form of a high-energy, extreme-ultraviolet (XUV) photon. Many electrons take part in thisprocess on each half-cycle of the driving laser field and the result is a broad distribution of kinetic energies at recombination and a correspondingbroad band of XUV emission. In the shortest drive laser pulses there are only a few half-cycles of the carrier electric field. At lower XUV photonenergies, these photons interfere with each other, resulting in a spiked structure in the measured spectrum (right). In contrast, the highest energyphotons are emitted in a single burst, by the electric-field oscillation with the largest amplitude, resulting in an interference-free, smooth drop-offat the highest photon energies. A filter is used to let through only those photons with high energies and a smooth spectrum, resulting in anisolated attosecond XUV pulse.090 100 110 120 130 140photon energy (eV)fem to second pump– probe experiments. Cur rently, inat tosecond spectro scopy only a single atto second pulseand the NIR drive pulse are available. Nevertheless,attosecond resolution can still be achieved using ameasurement technique now called the “attosecondtransient recorder”. The attosecond pulse is used totrigger the dynamics, while a much weaker replica ofthe drive-pulse electric field is used as a probe. Theattosecond transient re corder was first demonstratedby Ferenc Krausz and co-workers at the TechnicalUniversity of Vienna, Aus tria, in 2004 and has sincebeen the basis for many measurements made inattosecond spectroscopy.What we gainUltrafast lasers have been widely used in industry formicromachining parts, as no material can withstandthe intensity of a femtosecond laser pulse. Since only asmall amount of energy is used to reach these high in -tensities, only a tiny amount of material is removed witheach pulse, allowing for high-precision cutting. ThisAttosecond laser pulses canbe used to study atomic processesthat may be highly relevant toour understanding of howhuman cells become malignant andcancers develop50same property is also exploited in laser eye surgery.Originally discovered through an unfortunate laser eyeinjury, ultrafast laser pulses can deliver the preciseamount of energy required to break protein bonds inthe eye without affecting the surrounding tissue.Attosecond laser pulses, which are not only short butare also composed of high-energy photons, can be usedto study inner-shell atomic processes including relaxationfollowing ionization by energetic photons. Thestudy of these processes may be highly relevant to ourunderstanding of how human cells become malignantand cancers develop.In 2007 attosecond pulses were used by Krausz andcolleagues to probe one of the fastest distinct eventsyet recorded in the time domain. The researchers wereable to use attosecond spectroscopy to observe theindividual elementary steps of photoemission – theprocess by which electrons are emitted from a materialby light – namely excitation, transport and emission.In fact, electrons from the delocalized conductionbandstates were found to be emitted approximately100 as before the electrons from localized, deeplybound core states. It is not yet precisely clear why sucha delayed emission exists, but as photoemission is oneof the most fundamental examples of quantum me -chanics, experiments will continue until full understandinghas been gained.Fast forwardThere is a lot we can do with attosecond laser technology,but to make progress, such systems need to beused more widely. With their extremely short but relativelyweak pulses, attosecond laser systems complementlarge-scale “hard” (high photon energy) laserfacilities, such as the Linac Coherent Light Source atPhysics World May 2010

physicsworld.comThe laser at 50: Attosecond lasers and beyondGrasping timescalesEleftherios Goulielmakisone optical cycle( ~ 2.5 femtoseconds)Thorsten Naeser, Max Planck Institute of Quantum OpticsAs laser performance improves, the quantities that define it sound evermore impressive, with each successive prefix more exotic than the last. Forpower, the numbers become increasingly large – gigawatt (10 9 W),terawatt (10 12 W) and petawatt (10 15 W). Pulses, however, are getting evershorter – picosecond (10 –12 s), femtosecond (10 –15 s) and attosecond(10 –18 s). It is these short pulses from ultrafast lasers that are now lettingus explore processes on these timescales in real time.But these quantities can remain abstract, as it is difficult to relate themto anything in our daily lives. One second is a quantity with palpablemeaning, as it is roughly the time between beats of the human heart and isan interval that we can easily perceive. A picosecond, in contrast, is thecharacteristic time taken for molecules to move back and forth. We areactually able to sense these motions without any fancy instruments, as theyare responsible for the temperature of the air and everyday objects.Getting shorter, the femtosecond regime is the characteristic timescaleon which chemical reactions take place, or the time required for bondsbetween atoms and molecules to be broken and formed. Observing this inreal time has been called the “holy grail” of chemistry, letting us studyeverything from the storage and release of energy in batteries to thefundamental process of photosynthesis.And finally to the timescale that is the most recent barrier broken bypulsed lasers: the attosecond. On the attosecond timescale, even themaking and breaking of chemical bonds appear to occur slowly, and wouldbe akin to watching a slow-motion nature video of shoots unfurling theirleaves. In this regime, we are able to resolve charge dynamics – themovement of electrons between the energy levels of an atom, or ofelectrons or holes (electron counterparts) through an insulating interfacesuch as a p–n junction in a transistor.Physics World May 2010the SLAC National Accelerator Laboratory in the USand the European XFEL currently under constructionin Germany.As attosecond laser systems improve, they will let usaccess ever more complex systems and dynamics. Inmost experiments, a system can be prepared, its dy -namics triggered and subsequently observed every fewmicroseconds on a fresh sample to build up measurementstatistics. Therefore, ideally, attosecond laserswould pulse much faster at repetition rates higher thanthose that are currently possible. How ever, increasingthe repetition rate of current attosecond laser systemsis impossible owing to the heating that this causes inconventional laser gain media.In the future, it will be possible to use nonlinear opticsto move beyond the limits of standard laser gain mediain attosecond lasers. In a process called parametricamplification, the nonlinear response of certain transparentcrystals can be used to couple energy from onefrequency of light to another. For femtosecond pulses,parametric amplification can be used to transfer lightfrom a single frequency into a broad band of other frequencies,as is the case in Ti:sapphire. How ever, in contrastto traditional laser systems, during parametricamplification light is not strongly absorbed, so heatingis no longer a problem, allowing higher pulse repetitionrates and average powers. The average power outputof optical parametric amplifier (OPA) systems could beincreased to kilowatt levels. Further more, it is possibleto achieve even higher gain bandwidths in parametricamplifiers that allow direct amplification of quasi-fewcycleoptical light pulses, which is not possible in today’schirped-pulse amplification systems.OPAs can also be used to create HHG drive pulseswith different carrier wavelengths. The maximum photonenergy that can result from the HHG processdepends on the amount of kinetic energy that the ionizedelectron can accumulate while being accelerated inthe carrier laser field. The longer the electron travelsin the electric field, the more kinetic energy it has timeto amass, and the greater the emitted photon energy.This interaction time can be increased by using longerwavelengthdrive pulses. By moving to longer wavelength,ultrashort drive pulses, the photon energy ofisolated attosecond XUV pulses can be increased, thusallowing the efficient generation of pulses deeper inthe XUV or even in the “soft” (or low energy) X-rayregime. This is critical, as carbon absorbs XUV radi -ation at 284 eV making it visible, while water remainstransparent, allowing researchers to probe deep insideorganic materials with attosecond resolution on atomiclength scales.Looking further ahead, the development of a techniquecalled “quasi-phase-matching” may lead to atto -second light sources producing hard X-ray photonenergies and orders of magnitude more photons perpulse, which would allow these sources to compete withlarge-scale facilities. It has been predicted that thebandwidth of emission will also increase substantially,allowing for the generation of sub-attosecond, that iszeptosecond (10 –21 s), pulses, at which point it wouldbe safe to say that we have gone beyond ultrafast. ■51

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physicsworld.comThe laser at 50: Visions of the futureHank Morgan/Science Photo LibraryWhere next for the laser?From sharpening astronomical images and searching for gravitational waves to creating Bose–Einsteincondensates and measuring the properties of DNA, the laser has had a tremendous impact on manydifferent areas of science. Here, six experts recall how the laser has advanced their fields of interest –and speculate where the laser will take these areas nextAstronomyClaire Max is an astronomerand director of the Centerfor Adaptive Optics at theUniversity of California,Santa Cruz, USWe all know that turbulence inthe atmo sphere makes stars twinkle, but it alsoseverely blurs telescope images. Newton realizedthis back in 1730, when he wrote in Opticksthat “the Air through which we look upon theStars, is in perpetual Tremor… The only Rem -edy is a most serene and quiet Air, such as mayperhaps be found on the tops of the highestMoun tains above the Grosser Clouds”.Theoretically, telescopes of ever largerdiameter should be able to resolve eversmaller features within astronomical images.But the blurring due to atmospheric turbulenceis so severe that even today’s largestground-based telescopes (8–10 m in diameter)cannot see any more clearly than thesmall 20 cm backyard telescopes used byamateur astronomers on weekend evenings.To remedy this situation, astronomers haveturned to adaptive optics, a technology thatmeasures snapshots of the atmospheric turbulenceand then corrects for the resultingoptical distortion using a special deformablemirror (usually a small mirror placed behindthe main mirror of the telescope). Since thePhysics World May 2010turbulence is changing all the time, thesemeasurements and corrections must be donehundreds of times a second.Early adaptive-optics systems used lightfrom a bright star to measure the turbulence.However, most objects of astronomical in -terest do not have bright stars sufficientlyclose by, and hence the sky coverage of ad -aptive optics was quite limited. Then, in theearly 1980s, astronomers realized that theycould use a laser to make an artificial “star”as a substitute. This insight greatly extendedthe reach of adaptive-optics systems, sincelasers could be pointed in the direction ofany observing target in the sky. In the pastfive years these laser “guide star” adaptiveopticssystems have really come to fruition,to the point where today every major 8–10 mtelescope sports its own laser beacon.The lasers used in these beacons have re -spectable average powers of about 5– 15 W(a typical laser pointer, in contrast, has apower of less than 1 mW). Indeed, federalregulations require US observatories to turnthem off whenever aircraft approach; observatoriesalso file their observing plans inadvance with Space Command to avoid hittingsensitive space assets.Two types of laser predominate. The first isa custom-built system that is tuned to the yellow589 nm reson ance line of neutral so -dium, creating a guide star at an altitude ofabout 95 km by exciting naturally occurringsodium atoms in the Earth’s upper atmo -sphere. The second type is tuned to green oreven ultraviolet wavelengths and uses Ray -leigh scattering of atmospheric moleculesand particulates to create a guide star atan altitude of 15– 20 km. The advantage ofgreen and ultraviolet lasers is that they arecommercially available, making them muchcheaper to use than adaptive-optics systemsthat exploit yellow light.Thanks to laser guide-star adaptive optics,today’s 8–10 m telescopes have better spatialresolution at infrared observing wavelengthsthan the Hubble Space Telescope, simplybecause of the larger size of their mirrors.Proposed giant telescopes, such as the ThirtyMeter Telescope, the Giant Magel lan Tele -scope and the European Extremely LargeTelescope, all plan to use multiple laser guidestars at the same time. This will allow astron -omers to measure, and correct for, the turbulencein the entire 3D column of air abovethe telescope. These multiple-laser systemswill use the techniques of tomography – similarto those used in medical imaging’s computerizedaxial tomography (CAT) scans – toreconstruct the turbulence profile, enablingadaptive-optics correction over much widerfields of view than are available today.53

The laser at 50: Visions of the futurephysicsworld.comNew kinds of lasers with differentwavelengths, ever shorter pulse lengths,ever higher powers, ever narrower spectralwidths and ever better stability have allmade possible new kinds of experimentsWilliam D PhillipsAtomic physicsWilliam D Phillips is aphysicist at the NationalInstitute of Standards andTechnology (NIST) inGaithersburg, Maryland, US.He shared the 1997 NobelPrize for Physics with Claude Cohen-Tannoudji and Steven Chu for cooling andtrapping atoms with laser lightIn the early 1970s I was a young graduate studentin Dan Kleppner’s research group atthe Massachusetts Institute of Technology,working on a thesis that involved makingprecision measurements with a high-magnetic-fieldhydrogen maser (masers were themicrowave precursors to the laser, which wasoriginally called an “optical maser”). Klep -pner and Norman Ramsey had inventeda low-field version of the hydrogen masermore than a decade earlier, and the highfieldversion was producing unprecedentedlyaccurate measurements of magnetic mo -ments in atoms – a sort of zenith for this kindof atomic physics.But then came a new development thatwould change the direction of work in Dan’slab, in my career and in atomic physics as awhole: the first continuous-wave, commercial,tunable dye lasers. The lasing mediumin these devices was an organic dye that lasedover a far wider range of wavelengths than,for example, a helium–neon laser, wherethe gain medium is an atomic gas. The introductionof these devices meant that eventhose who were not experts in laser designand construction could, by tuning a laser toan atomic-resonance transition, explore anew domain of atomic manipulation whereco herent light was the key tool.Eager to play with these new toys, I askedDan to suggest an additional thesis experimentusing lasers. He agreed, and suggestedthat I study collisions of optically excitedsodium atoms. I began to build the apparatus.Other students and postdocs in thegroup started new experiments as well. Eachissue of the research journals brought anincreasing number of laser-related papers,and each conference saw reports of newlaser experiments.The excitement of that time was palpable.New ideas and new experiments popped upeverywhere. In 1978 I was inspired by DaveWineland’s demonstration of laser coolingof ions at the National Bureau of Standards(now NIST) in Boulder, Colorado, and byan idea from Art Ashkin at Bell Laboratoriesto slow and trap a beam of sodium atoms.Later that year, when I went to the bureau’slabs in Gaithersburg, Maryland, I took mythesis apparatus with me and began to workon laser cooling and trapping of sodium.For me, the excitement I felt in the 1970sin Dan’s lab has never waned. New kindsof lasers with different wavelengths, evershorter pulse lengths, ever higher powers,ever narrower spectral widths and ever bet-54ter stability have all made possible new kindsof experiments. Laser cooling of many moretypes of atoms and ions, plus giant coldmolecules, atomic clocks ticking at opticalfrequencies, and non-classical states of lightare just some of the paths into which lasershave led atomic, molecular and optical(AMO) physics.Moreover, lasers have allowed AMO phy -sicists to realize Bose–Einstein condensation,to create optical lattices and to studyultracold Fermi gases. Each of these hasdeepened the connections between AMOand condensed-matter physics. It may bethat lasers and cold atoms will help to elucidatesome of the outstanding problems incondensed matter, such as the origins ofhigh-temperature superconductivity and thenature of fractional-quantum-Hall statesthat are useful for quantum computing.Ever since they first became available,lasers have invigorated and reinvigoratedatomic phys ics, and the adventure shows nosigns of stopping.BiophysicsSteven Block is abiophysicist at StanfordUniversity, California, USOver the past 10 years, it hasbecome possible to do ex -peri ments in biophysics thatwere previously just pipe dreams. For ex -ample, I work in a field known as single mo -lecule biophysics. In this area, the challengeis to study the molecules of life – the proteins,nucleic acids, carbohydrates and other chemicalsthat make us up – literally one moleculeat a time. This is not easy to do, because allbiomolecules are much too small to be seenusing, say, a conventional microscope. None -the less, we are finding that they can bemanipulated and measured, and the techniquesthat are in volved in doing this oftenrequire lasers.One technique that my lab has helped topioneer is known as “optical tweezers”. Theidea behind optical tweezers is that you canuse the radiation pressure supplied by aninfrared laser beam to capture and manipulatesmall materials – including individualproteins and nucleic acids – and move themaround under a microscope. To do this, wehook tiny microscopic beads up to moleculessuch as DNA. Then we can use opticaltweezers and optical traps to “hold onto”these beads and exert very tiny, controlledforces on the DNA molecules.The lasers that we use for this have somepretty extraordinary properties – they arenot like the laser in a laser pointer or in yourCD player. We need to be able to hold a laserbeam stably in space to within the diameterof a hydrogen atom, or about 1 Å, for severalseconds at a time. This is because the basepairs in a DNA molecule are only separatedby about 3.5 Å, and one of the things we areinterested in studying is how the enzymeRNA-polymerase, which “reads” the geneticcode, moves as it climbs the DNA ladder onebase pair at a time.It is amazing that we can literally watch thishappen, and it all depends on being able toshine laser light on the enzyme, scatter thatlight and measure displacements that areaccurate down to an angstrom. We are constantlylooking for lasers with higher powerin single modes and better stability prop -erties. Some of the new generation of diodelasers are now reaching the point where theycan be used for these ex peri ments, but for themost part they have not made it out of the labyet. It will be very interesting once they do.DefenceJeff Hecht is a freelancescience and technologywriter based in Auburndale,Massachusetts, US, whohas covered laser weaponssince 1980High-energy laser weapons – long the stuffof science fiction – have recently reached aturning point. But it is not the one you wouldexpect if you saw news clips of a laser-armedBoeing 747 shooting down a target missile inFebruary this year. Instead, the US military isplanning to concentrate on thwarting attacksfrom short-range targets such as rockets,mortars and artillery shells.Modern laser weaponry dates from about1980, when the main goal was to develophigh-energy lasers capable of destroyingmissiles launched hundreds or thousandsof kilometres away. Indeed, US PresidentRon ald Reagan’s “Star Wars” programmespent billions on plans for orbiting laser battlestations. But tough technology problemsPhysics World May 2010

physicsworld.comThe laser at 50: Visions of the futureand the end of the Cold War changed the re -quirements. The result was the Air borneLaser (ABL): a Boeing 747 equip ped with amegawatt chemical oxygen– iodine laser anddesigned to shoot down missiles launchedby a “rogue state”.But in May 2009, US defence secretaryRobert Gates reported that the ABL (longplagued by budget and deadline overruns)had a lethal range of less than 140 km – farshort of the planned minimum of 200 km. So,after the current round of tests (conductedat an undisclosed shorter range), efforts toreach megawatt powers will start again withlasers that use diode-pumped alkali-metalvapours. Lasers of this type currently emitjust tens of watts but may eventually offer abetter power-to-size ratio than the ABL.Until those plans get off the ground – ifthey ever do – the bold new future of laserweapons will be solid-state lasers that emit100 kW or more in a steady or repetitivelypulsed beam. It has already been demonstratedthat kilowatt-class lasers can detonateunexploded ordnance left on the battlefieldby illuminating it from a safe distance. Thehope is that lasers in the 100–400 kW rangecould also destroy rockets, mortars and shellsat distances of up to a few kilometres. Theclose range of these targets would greatlyease beam-propagation problems that hamperlaser-based missile-defence systems.More over, by detonating explosives in the airwith laser heating, rather than firing pro -jectiles at them, laser-based weapons couldreduce “collateral damage” to friendly soldiersand non-combatants.In March 2009 US defence giant NorthropGrumman reported continuous emission ofmore than 100 kW for five minutes from alaboratory diode-pumped laser. This Feb -ruary, Textron Systems reached the samegoal with its own design. These are by far thehighest continuous powers achieved in asolid-state laser. The next step will be toengineer a 100 kW laser that works on ships,trucks and planes. The US Army is movingNorthrop Grumman’s device to the HighEnergy Laser System Test Facility at theWhite Sands Missile Range, New Mexico,where it is planning to try out a mobile versioninstalled in a heavy battlefield truck. An -other defence agency, DARPA, is building alightweight 150 kW solid-state laser for usein fighter planes, while the US Navy is planningtests of similar lasers at sea.The lasers used in all these projects marka radical departure in laser-weapon design.Earlier weapon-class lasers were chemicallyfuelled, but commanders did not want themon the battlefield because handling chem -ical fuels posed major logistical issues. Theyalso wanted lasers that could be poweredby diesel generators. But other formidablechallenges remain, including damage to thelaser itself, the need to operate in a dirty battlefieldenvironment and the expected highcost of the devices.Physics World May 2010Honolulu Star BulletinBagging a few test rockets should be easy.Engineering mobile lasers that work reliablyin messy places where people are shootingat them is a much tougher problem. We willprobably see prototypes blasting targets outof the sky within a few years, but do not ex -pect battlefield deployment until the 2020sat the earliest.Free-electron lasersJohn Madey is director ofthe FEL Laboratory at theUniversity of Hawaii, US,and contributed to thedevelopment of freeelectronlasersLike all lasers, free-electron lasers (FELs)rely on the principle of stimulated emissionto amplify a beam of light as it passes througha region of space. In other words, as electronsmove from a high- to a low-energystate, they emit photons of light all at thesame wavelength and all moving in the samedirection. But unlike the transitions betweenbound electronic states in other lasers, FELsexploit another of Einstein’s key discoveries– special relativity – to provide tunable electromagneticradiation from a beam of relativisticfree electrons as they move througha spatially periodic transverse magnetic field.According to special relativity, the electronsperceive such a field as an intensetravelling wave in their rest frame, with awavelength reduced in proportion to theirkinetic energy. Photons scattered by the electronsfrom this pulse in the direction of theirmotion are reduced in wavelength once againwhen viewed from the laboratory frame. Asa result, electrons with a kinetic en ergy of50 MeV emit near-infrared radi ation whenmoving through a field with a period of 2 cm.Light of longer and shorter wavelengths canbe created by simply varying the energy ofthe electrons. FELs can readily provide laserlight with about 1% of the instantaneouspower of the electron beam – megawatts ormore – and their pulse lengths can vary fromless than a picosecond to full continuouswaveoperation. Ex cep tional phase coherenceis also attainable through the use ofsuitable interferometric resonator systems.Serious efforts to explore the possibleapplications of FELs began shortly aftercolleagues and I at Stanford University successfullydemonstrated the first opticalwavelengthFEL amplifiers and oscillatorsin 1974 and 1976, respectively. The focussince then has been on using FELs to dothings that are tricky to pull off by othermeans. Perhaps the best known applicationis to generate tunable, high peak power,coherent, femtosecond X-ray pulses at energiesabove 1 keV to carry out time-resolvedstructural and functional studies of complexindividual and interacting molecules. Thefirst such X-ray FEL is now in operation atthe SLAC National Accelerator Laboratoryin the US, with the European X-ray Free-Electron Laser due to come online at theDESY lab in Germany in 2014.Even for applications where other types oflasers might be adequate, the big advantageof FELs is that they are so flexible. FELshave therefore proved invaluable in carryingout exploratory research when the requirementsof a particular application have not yetbeen determined or when a research teamdoes not have the time or money to developa new specialized laser system needed to supportthe application. The short-pulse, highpeak-power,third-generation FELs, whichwere pioneered in the 1980s, have beenpartic ularly useful for developing new surgicaltechniques and for exploring the energylevels, band structure and mobility of electronsand holes in new electronic and opticalma terials, without having to worry aboutlonger probing laser pulses damaging thematerial.The more recently developed high-average-powerFEL systems have extended thesecapabilities to include research on possiblelaser applications for industrial-scale ma -terials processing. Of at least equal signi -ficance are the improvements in remotesensing for climate-change research madepossible by the broad tunability, high peakpower, and exceptional spatial and tem poralcoherence offered by FELs at visible andinfrared wavelengths.There are, however, a few clouds on thehorizon for FEL research. Historically, suchresearch has mainly taken place at a handfulof small and mid-sized university and governmentlabs in the US, Europe and Asia. Arecent transition to larger national labs hasbrought many scientific advances, but alsoruns the risk of making both the science andShort-pulse, high-peak-power,third-generation free-electron lasers havebeen particularly useful for developingnew surgical techniques and for exploringnew electronic and optical materialsJohn Madey55

physicsworld.com56the technology less accessible to universityscientists, who may be based far away fromlarge central facilities. It will, therefore, becritical to ensure that the customer and supportbase for the technology remains awareof the FEL’s smaller-scale applications, notjust the signature high-power and shortwavelengthones.Finally, there are concerns that the suppliersof FEL-supporting technologies – in -cluding high-power microwave, ultra-highvacuum and special optical materials – maynot be able to continue these product lines,given the decreasing industrial markets forthem. Wise governments should take thesteps needed to ensure that the know-howon which these critical national capabilitiesrely is not lost.Gravitational wavesEric Gustafson is at theCalifornia Institute ofTechnology, US, and leadsthe instrument- science groupof the LIGO gravitationalwaveobservatoryOften referred to as “ripples in space–time”,gravitational waves are generated duringextremely violent astrophysical events inwhich the velocities of objects such as neut -ron stars or black holes change by substantialfractions of the speed of light over a verybrief period of time. Detecting such waves isa challenging task because, for ground-baseddetectors, these changes in velocity occur ontimescales between a fraction of a millisecondand a few tens of milliseconds. Meas -uring these tiny fluctuations in the curvatureof space–time requires the use of very sensitivelaser interferometers, in which beams oflight travel down the perpendicular arms ofthe device, bounce off mirrors at the far endof each arm and then return to interfere withone another. The idea is that a passing gra -vitational wave should change the interferencepattern in a characteristic way.As laser technology has evolved, the lasersused in gravitational-wave experiments havechanged with it. The first interferometric ex -periment designed to detect these waves,built by Robert Forward at California’sHughes Research Laboratory in the early1970s, used a 75 mW helium–neon laser andwas about the size of a chessboard. Forwardreached an impressive sensitivity with thisdevice, measuring the smallest vibrationaldisplacement that had been detected with alaser to date: 1.3 × 10 –14 m Hz –1/2 – equivalentto measuring changes of less than 2 mm inthe distance from the Earth to the Sun. How -ever, the poor power-scaling properties ofthe helium–neon laser meant it did not havea future in gravitational-wave interferom etrybeyond table-top experiments.During the 1980s, several groups aroundthe world built interferometers in ultra-highvacuumsystems, with their optics suspendedto isolate them from ground noise. These ex -periments were between one and a few tensof metres in size and used argon-ion lasers,which operate at a wavelength of 514 nm andoutput several watts of power. Such interferometerswere usually designed to studyspecific problems in gravitational-wave in -terferometry, such as comparing differentoptical configurations, finding ways to controlthe suspended optics and characterizenoise in subsystems such as mirrors, and de -veloping length and alignment control signalsfor the suspended optics.Unfortunately, the plasma tubes used inargon-ion lasers, along with the cooling waterthey require, produce high levels of laserfrequencynoise. What is more, the relativelyshort lifetimes of these tubes made them im -practical for use in an observatory. Finally,the power output of the lasers – while higherthan a helium–neon laser – was short of thehundreds of watts that more advanced detectorswere understood to require, thanks tothe fact that at high frequencies the detectorsensitivity is limited by shot noise.In the 1990s, as the current group of kilometre-scaleobservatories (LIGO in the US,VIRGO in Italy and GEO in Germany)were being planned and built, diodepumpedsolid-state lasers became available.These lasers not only had much lower levelsof frequency noise than argon-ion lasers,but also the potential to produce muchhigher power. Initially, their maximumpower output was about 10 W, but improveddiode-pumped lasers and the use of injection-lockedpower oscillators or masteroscillatorpower-amplifier configurationsmade 100 W-class lasers possible for a newgeneration of interferometers. These newinterferometers will be deployed over thenext few years at LIGO and VIRGO, andwill use 200 W lasers. Mean while, GEO willuse a squeezed-light technique to producebet ter shot-noise performance at lowerlaser power. For space-based instrumentssuch as the Laser Interferometer SpaceAntenna (LISA), diode-pumped solid-statelasers were selected not for their high powerpotential but for their very high efficiencyand reliability, characteristics that are especiallyimportant for a space-based mission.It is not clear exactly what lasers or wavelengthswill be required for future groundbaseddetectors. We may see slightly longerwavelengths selected that can be used withnew mirror-substrate materials that areopaque at 1064 nm; equally well, we mightsee shorter wavelengths that allow us to usethinner mirror coatings, thus reducing thethermal noise produced. It is possible thatas researchers begin to look for the “right”wavelength to optimize sensitivity, we willfind that we need wavelengths that can onlybe produced via the nonlinear frequencyconversion of solid-state lasers – and so ourchoice of lasers may continue to evolve.■Physics World May 2010

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physicsworld.comCareersSupportinglaserscienceIf the laser in your laboratory isnot working, your first port ofcall (after the instructionmanual!) will be someone likeHarald Ellmann, whosefascination with practicalproblem-solving led to a careerin technical supportThe end of the line Harald Ellmann’s job allows him to contribute to science by solving other researchers’ problems.I first heard the phrase “a physicist can doanything” when I was pondering my optionsafter I finished secondary school. But evenafter I finally decided to embark on a degreein physics, I could not have imagined howtrue this would be. In my case, although Istarted out wanting to be a scientist, physicshas instead led me to a career that involveshelping scientists solve problems, as the servicemanager of a medium-sized laser firm,Toptica Photonics.My undergraduate studies took placeat the Ludwig-Maxmilians-Universität inMun ich, Germany, during the early 1990s,but I did my diploma thesis externally atSweden’s Stockholm University. As a memberof the new laser-cooling project there,my task was to set up an experiment almostfrom scratch. One important aspect of thiswork was to build inexpensive diode lasersand the electronics needed to control them.One year into the project it dawned on methat I had not done any real science yet. Bythen, my aspiration was to be a scientist, andI therefore decided to take the next step bydoing a PhD in the same research group.In the years that followed, however, I discoveredthat instead of being attracted toproblems of fundamental physics, I wasmore keen on overcoming the technicalhurdles that prevented the experimentsfrom working.After I finished my PhD, I had to decidewhat to do next. Fortunately, I came acrossan advertisement from Toptica, which waslooking for a physicist to be its service manager.The company was certainly not un -58known to me; in fact, by the time my re searchcolleagues and I had finished our first re -liable diode-laser systems in the late 1990s,we received flyers from a start-up firmnamed “TuiLaser” (which eventually be -came Toptica) advertising almost the samelasers that we had just built. Thus, the jobrequirements were an almost perfect matchwith my skills, and after seven years inSweden I re turned to Munich.Troubleshooting for physicistsWhen Toptica began trading in the mid-1990s, its core market consisted of governmentinstitutes like the Max Planck Instituteof Quantum Optics or the Physikalisch-Technische Bundesanstalt that were in -volved in the rapidly evolving field ofexperimental quantum optics. Since then,the product portfolio has expanded fromdiode lasers to fibre lasers and optical-storagetesters, which are devices used to checkMost of my time isdedicated to support:if someone’s laseris not working, thenI am one of thepeople they callthe reproduction quality of Blu-ray discs atmass-production sites. The customer basehas broadened too: in addition to institutesand universities, it now also spans a steadilygrowing range of industrial partners, withapplications in materials processing, micro -scopy and optical-storage technology.Despite this, the scientific market still representsthe core of Toptica’s business. Oneconsequence of this is that the firm is followingan “open” approach to laser design,meaning that its customers have nearly unrestrictedaccess to the inner workings of theirlasers, so that they can adapt their devices totheir individual needs. As a result, most ofmy working time is dedicated to direct technicalsupport: in other words, if someone’slaser is not working, then I am one of thepeople they call. In addition to helping troubleshootproducts, in quite a few cases I alsoact as an application advisor – offering suggestionson, for example, schemes for activefrequency stabilization. Here it is certainlyhelpful to be able to tap into the vast pool ofknowledge within Toptica: about 25% of my85 colleagues have a PhD, predominantly inphysics, and more than 50% of all em ployeeshave an academic background in either phys -ics or engineering.The other important side of my job as “servicemanager” is to establish customer serviceas a distinct entity within the company.In a nutshell, this means I am working onintroducing structure and scalability into thefirm’s service processes so that we are preparedfor the ongoing growth of the company.We have, for example, implemented aPhysics World May 2010

physicsworld.comCareersmonitoring system that allows us to keeptrack of repairs, so we always know the statusand the history of each product. This enablesus to analyse our records and detect sys -tematic problems, and thus provide valuablefeedback to product management and R&D.The next step will be to implement a ticketsystem that also keeps track of communicationswith individual customers. This is somethingthat will become really import ant assoon as the number of support em ployeesexceeds the current head count of two.This kind of structural, long-term workrequires a certain amount of attention and“focus”, but my day-to-day work most ofteninvolves the exact opposite: namely, I needto react rather than act. There is a constantinflux of service requests and at times my colleagueand I have to juggle 10 or more ofthese without dropping a single one. Unlikein science, where one usually concentrateson a certain problem for an extended periodof time, in my role things tend to get blurryrather than focused. Finding the time towrite this article, for example, required acombination of time management and luck:I happened to encounter a relatively quietphase when my attention was not beingpulled in different – and often diametricallyopposite – directions.Working in a mid-sized hi-tech companyis a big challenge for those of us involved insupport because the firm’s products arediverse and the cycle for innovations is short.In order to stay ahead of the curve commercially,the firm is constantly developing, marketingand selling new products. At Toptica,many of the products are customized, so weneed to bring ourselves up to date all thetime. This means that very often I am confrontedwith problems I have not heard ofbefore; in fact, there have even been a fewoccasions when customers have called askingfor help with a product that I did notknow even existed!In addition to these technical challenges,my work requires patience, communicationskills and empathy. It is important to remainaware of the fact that behind each technicalissue there is also a real person with a problem.Working in support also means thatmost often one is confronted with weaknessesand flaws in products rather thanstrengths, and at times it can be hard toshoulder the collective responsibility for,say, a faulty laser. On the other hand, it is im -mensely rewarding to be able to quickly helpa student who has become stuck in the middleof an important experiment. So, ul -timately, I do contribute to scientificpro gress – just in a rather more subtle waythan I had originally imagined.Harald Ellmann is the service manager forToptica Photonics in Graefelfing, Germany,e-mail harald.ellmann@toptica.comOnce a physicist: Fausto MoralesPuzzle-games designerFausto Morales describeshis career as “a nomadicadventure in pursuit ofinteresting problems”.His book Zigzagrams waspublished by AuthorHousein 2009Why did you decide to study physics?While reading books like Paul Davies’ The Edge ofInfinity, I gradually felt the urge to explore the lawsthat rule our universe. I anticipated a fascinatingjourney filled with beauty on both sides of the road,and my dream came true in the late 1980s thanksto the extraordinary faculty and curriculum atSonoma State University in California. As anundergraduate student there, I had the rareopportunity to engage in serious research onbinary-star systems. Once I started doing graduatework at the University of Michigan, this experienceenabled me to work in a high-energy-astrophysicsresearch team led by James Cronin, who shared the1980 Nobel Prize for Physics.What led you to switch to pure mathematics?A superb graduate series of lectures on grouptheory for physicists, taught by Karl Hecht atMichigan in 1990, helped me realize that I wasbetter equipped to understand and enjoy algebraicstructures in pure form, devoid of the complexityintroduced by their advanced applications inphysics. By the end of the course, I concluded that Ihad become far more interested in groups for theirstructural properties than for their contributions totheoretical physics. It was time for me to switchgears and explore group theory.What did you do next?My eclectic academic background – anundergraduate physics degree, graduate work inphysics and computer science, and finally adoctoral programme in pure mathematics – hasallowed me to hop from one field to the nextwhenever I have been tempted by an interestingchallenge. Initially, I used physics, mathematicsand object-oriented computer programming totackle intriguing problems for the aerospaceindustry, such as automating aircraft routegeneration to maximize pilot safety in hostilescenarios. Next, I worked on speech-recognitionsystems aimed at automating the interpretation ofmessages uttered by humans, without help fromintervening menus. Then I moved on to developdata-mining methodology, mainly for financialapplications, an activity that I currently juggle withlogic-game design.What are zigzagrams and how did you comeup with them?A zigzagram is an extension of Sudoku. Eachcolumn and row in a zigzagram contains thenumbers from one to nine, but with the additionalcondition that every compartment must contain anodd number of odd numbers. Because the newcondition would be redundant in the familiarsquare-box partition, zigzagrams incorporatecompartments of varying sizes – named“zigzagons” because of their twisting appearance.The rule about odd numbers introduces a newdimension into the thinking mix, enhancing the“systematic search” themes of Sudoku bycombining them with elementary ideas that emergefrom the logical implications of this odd–evenparity rule.What are you working on now?In my “day job” I am currently working as anindependent consultant on decision algorithms forfinancial applications such as e-trading. But I amalso progressing towards publishing two othernumber-placement games that, like zigzagrams,involve repartitioning the 9 × 9 square andextending the rules of Sudoku so as to provideplayers with a wider variety of logical themes to mixinto their reasoning processes.What was it that sparked your interestin puzzles?It must be innate, since I have always enjoyedsolving original problems. I like chess puzzles justas much as word or number puzzles, as long as theycall for creativity.If you could offer one piece of careersadvice to physics students today, whatwould it be?I would say, quoting Albert Einstein, that “inmoments of crisis, only creativity is more importantthan knowledge”. All physics graduates have beenthoroughly trained to adapt to any kind of jobmarket – and even thrive in it – by virtue of theirsuperior ability to tackle new problems. I think thatan open mind is the best career asset for a physicsstudent today.● www.zigzagrams.comTo make the most of your physics degree, visitwww.brightrecruits.comPhysics World May 201059

Careersphysicsworld.comCareers and peopleUK grants for ‘world’s best’ studentsUp to 100 research students will have theirfees and expenses part-funded by the UKgovernment as part of a £2.5m scheme toattract talented students from aroundthe world to UK universities. TheNewton Scholarship programme will provide£25 000 each to 100 highlyskilled candidates who wish to pursuepostgraduate studies in the UK. Withmedian annual tuition fees reaching£11 900 for overseas students onlaboratory-based research courses in 2009,the new scholarships will not, however,cover the full cost of a PhD. Nevertheless,the director of the Russell Group of eliteuniversities, Wendy Piatt, praised thescheme, calling it a “welcome initiative”in the face of “increasingly fierce globalcompetition” for top students. The firstNewton Scholars are expected to begintheir studies in the autumn.New chief for French nuclear physicsJacques Martino has been appointeddirector of the National Institute ofNuclear and Particle Physics (IN2P3), theumbrella group for elementary particlephysics within CNRS, France’s nationalscience agency. Martino, an experimentalnuclear physicist, has led the Subatechnuclear-physics laboratory at theEcole des Mines de Nantes since 2001, andhas also served on numerous scientificpolicycommittees since gaining hisdoctorate in 1982. As head of theIN2P3, he will oversee operations at32 laboratories (most of which are run inconjunction with universities in France)and 40 international projects, with acombined budget of about 745bn.He replaces the particle physicistMichel Spiro, who was elected president ofthe CERN council in December 2009.GPS pioneer honouredA physicist whose method for trackingSoviet satellites during the height of theCold War evolved into the modernGlobal Positioning System (GPS) has beeninducted into the US National InventorsHall of Fame. Roger L Easton, who beganhis career at the Naval ResearchLaboratory during the Second World War,was honoured for developing and testingthe concept of “time navigation”:exploiting the accuracy of space-borneatomic clocks to pinpoint the location andtrajectory of objects on Earth. Initiallyintended for the military, GPS devices arenow found in numerous civilianapplications, including sat-navs in cars.Movers and shakersThe CERN theorist John Ellis hasbeen appointed Clerk MaxwellProfessor of Theoretical Physics atKing’s College London.Herbert Mook Jr of the Oak RidgeNational Laboratory has won theNeutron Scattering Society of America’sClifford E Shull Prize.The Astronomical Society of the Pacifichas awarded its top prize, the Bruce GoldMedal for lifetime achievement inastronomy, to Gerry Neugebarger of theCalifornia Institute of Technology.The 2010 Grote Reber Gold Medal forradio astronomy has been awarded toAlan Rogers of the Massachusetts Instituteof Technology’s Haystack Observatory.Space scientist Alan Title of LockheedMartin has been inducted into theSilicon Valley Engineering Hall of Fame.Next monthin Physics WorldTackling cancerEfforts to understand cancer have traditionally involvedviewing it in terms of chemistry and genetics. But physicistsare now bringing their expertise to bear by consideringliving cells as mechanical objects that can be controlledArizona State UniversitySymbols of powerTheoretical physicists have long sought to describe theuniverse in terms of equations. Could a new class ofsymbols, known as adinkras, be the way forward?Fits and startsFor two years Albert Einstein blocked Theodor Kaluza frompublishing what became the foundation for string theory.This, it turns out, was partly due to the human behaviour ofprioritizing, which results in delays and bursts of activityPlus News & Analysis, Forum, Critical Point, Feedback,Reviews, Careers and much morephysicsworld.com60Physics World May 2010

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physicsworld.comRecruitmentRecruitment AdvertisingPhysics WorldIOP PublishingDirac House, Temple BackBristol BS1 6BETel +44 (0)117 930 1264Fax +44 (0)117 930 1178E-mail sales.physicsworld@iop.orgwww.brightrecruits.comThe place for physicists and engineers to find Jobs, Studentships, Courses, Calls for Proposals and AnnouncementsDepartment of PhysicsLecturer (Centre for Graphene Science)£36,715 - £43,840 per annumAs a result of winning a multimillion pound EPSRC/HEFCE Science& Innovation Award, the Universities of Bath and Exeter haveestablished a national Centre for Graphene Science. The Centreis bringing together internationally leading research teams withinterdisciplinary expertise to work on: novel methods of producing,patterning and functionalising graphene; experimental and theoreticalstudies of graphene-based systems; the development of newgraphene-based electronic, photonic, chemical, bio- and medicaldevices and sensors.You must be able to establish an independent research programmein graphene science that effectively interfaces with the advancedinfrastructure available in Bath. This focuses on state-of-the-artlow temperature scanning probe-based characterisation andnanopatterning in addition to more conventional “top-down”nanofabrication tools.Reporting to the Head of Physics, you will play a key role within theBath team, building on research strengths demonstrated in the lastResearch Assessment Exercise when the Department was rankedamongst the top 5 Physics Departments in the UK. You should havea PhD in a relevant discipline and a demonstrated track record ofexcellence in materials-related research; experience in graphene orother carbon-based systems is especially welcome. Researchers inthe early stage of their careers are particularly encouraged to apply.Applications should be accompanied by a 1 page outline describingnovel research plans that would complement and enhance researchin the Centre.For further information and to apply online please visit our website atwww.bath.ac.uk/jobs quoting reference JK26.Informal enquiries should be addressed to Professor Simon Bending,(S.Bending@bath.ac.uk or +44 (0)1225 385173).Closing date: 31st May 2010.www.bath.ac.uk/jobsOclaro is a Tier 1 provider of innovative optical and lasercomponents and solutions for a broad range of diversemarkets, including telecommunications, industrial,consumer electronics, medical and scientific applications.Headquartered in California, we enjoy global presence andare poised for further growth.For our R&D and manufacturing site in Zurich, we arelooking forPhysicists / Engineersto help us meet increasing demand for our products.What we look for: semiconductor manufacturing, 6-sigma, RF design,LabView. industry.What we offer: you to take on responsibility from the beginning andwhere flat hierarchies encourage open communication. recruitment_zh@oclaro.com.Check out www.oclaro.com and find out more about us!Oclaro is an Equal Opportunities Employer.Leading the way in magnet technologyNMR Magnet - Project Engineer/DesignerMagnex, a wholly owned subsidiary of Varian, Inc. is a successful,high technology company, involved in the design and manufacture ofsuperconducting magnet systems for Magnetic Resonance and otherscientific applications.The advertised position is a technical role, involving extensive interactionwith many parts of the company and some with suppliers and customers.The applicant should be trained to at least degree level in a relevant (scientificor engineering) discipline. A PhD and/or industrial experience would beadvantageous. Some experience of magnet design, superconductors,cryogenics or NMR would be of particular benefit.Oclaro 15x2 May 2010.indd 1 19/4/10 12:33:43The applicant will be expected to demonstrate proven ability for innovationand/or product design and development, desire to work within an existingstrong team, ability to handle projects from conception to install, to work todeadlines and to manage a number of projects concurrently.To be considered for this opportunity, please send an up-to-date CV with acovering letter to either emma.reed@varianinc.com, or for the attention ofthe Human Resources Department at the address below.magnex scientific ltd – the magnet technology centre: 6 Mead Road,Oxford Industrial Park, Yarnton OX5 1QU,Tel: 01865 853800www.magnex.com www.varianinc.com62Physics World May 2010PWMayClMagnexVarian7x4.indd 1 19/4/10 12:39:49

Oxford Instruments provides high technology tools and systems forindustrial and research markets, based on our ability to analyse andmanipulate matter at the smallest scale. We are a global companywith offices and manufacturing sites in over 25 locations world-wideand a turnover of £200m.Our NanoAnalysis business is a global leader in advanced analyticalsystems for X-ray microanalysis and electron backscatter diffraction.The growth and development of this business has resulted in somevery exciting opportunities:Customer Services Business ManagerMarketing of our international service products.Product ManagerManage the lifecycle and product roadmap for our EDS products.Senior Software EngineerDeveloping the graphical user interfaces and software componentsfor high technology products using C#, Visual Studio and WPF.To apply, please send a copy of your CV to vicki.potter@oxinst.comquoting reference PWOINA1904. For more details and other excellentopportunities visit our website,The Business of Science.Oxford Instruments NanoAnalysisHalifax Road, High Wycombe,Bucks, HP12 3SETel 01494 442255www.oxford-instruments.comBell Labs, the innovation engine of Alcatel-Lucent, is a worldwideresearch and development community that focuses its efforts on keytechnologies for telecommunications. It is internationally renowned as thebirthplace of modern information theory, the transistor, the laser and theUNIX operating system.Bell Labs IrelandBell Labs’ research facility in Dublin, Ireland is a leading end-to-end systemsand solutions lab working in the areas of thermal management, wirelesssensor networks, autonomic networking, semantic data access, and servicescentricoperations research.Thermal Management /Eco-SustainabilityTechnical ManagerWe have an opening for a Technical Manager to lead a research teamworking in thermal management and related eco-sustainability aspectsof communication systems. The position involves the development andexecution of a research programme to delivery significant energy savings intelecommunications equipment.To be considered for this position, you should have a PhD in a related areaand a proven track record in research or strong industrial experience.A successful candidate will also have strong experience in crafting andimplementing a strategic vision for research as well as excellence in teamleadership.To apply and to obtain, further detail on the role profile, please contact byemail Elena Gonzalez (Elena.Gonzalez@alcatel-lucent.com). A comprehensivebenefits package exists, including relocation costs.See also http://www.alcatel-lucent.com/wps/portal/BellLabs/Ireland for furthercareer opportunities and information on Bell Labs Ireland.Oxford_13x2.indd 1 20/4/10 08:37:55Visit a host of free features tohelp you with the first step inyour new life: *Terms and conditions apply As CERN’s Large Hadron Collider opens up a new high energyfrontier, the Organization is pursuing advanced research anddevelopment for an electron-positron linear collider to exploitthe anticipated discoveries and further the understanding of theunderlying physics.In order to lead, coordinate, and liaise the studies of bothaccelerator and detectors, the linear collider community at CERN islooking for aLinear Collider Studies LeaderYour main responsibility will be to lead the linear collider workat CERN in a new project phase. You will also have a strategicinternational role to participate in shaping the linear collider anddetector landscape beyond the host Organization. Reporting directlyto the CERN Directorate and the CLIC/CTF3 collaboration board,you will engage with other laboratories to strengthen the currentcollaboration. Within this framework you will drive the R&D andprototyping work with a view to the production of a TechnicalDesign Report.Already having extensive leadership and project managementexperience with international renown in the field of particlephysics, you will have successfully led large collaborations requiringinteractions with both research and industry.Details of the vacancy, application process and employmentconditions can be found at:www.cern.ch/lcslPhysics World May 2010 63

The Max-Born-Institute for Nonlinear Optics and ShortPulse Spectroscopy (www.mbi-berlin.de) is part of theForschungsverbund Berlin e.V.” and is a member of the“Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz (WGL)”.In Division B: Light Matter Interaction in Intense Laser Fields(Director: Prof. Dr. W. Sandner) a position is offered for adoctoral studentin the field of experimental atomic and molecular physics.The position is immediately available for a 3-years term. Thesuccesslul applicant will work on a project funded by the “DeutscheForschungsgemeinschaft” (DFG). The specific field of researchwill be the investigation of the interaction of aligned moleculeswith high intensity ultra-short laser pulses at large internuclearseparation.Applicants should hold a university degree equivalent to theGerman diploma or a master degree and have good knowledge inatomic and molecular physics, ultra-short pulse laser techniques,or photo-electron/ion spectroscopy.Applications referring to the ref. no. 3-b2 should be addressed to:Dr. H. Rottke, Max-Born-Institut, Max-Born-Str. 2a, 12489 Berlin,Germany, Tel.: +49-30-6392-1370, e-mail: rottke@mbi-berlin.de,preferably by e-mail.64Faculty Search: Condensed Matter Physics,Biophysics and Quantum OpticsThe Nanyang Technological University (NTU), an excellence-driven researchuniversity in Singapore, is inviting candidates with internationally proven trackrecords to apply for positions at the Associate or Full Professor levels in the Divisionof Physics and Applied Physics. Candidates with potential for distinction may alsoapply for tenure track positions at the Assistant Professor level.We are looking for experimental and theory applicants whose research agendacomplements existing departmental strengths, including• nanoscale materialset your obs noticedwith our eaturedrecruiter option.• correlated electron systems• integrated science interfacing with related disciplines, and• quantum opticsFor the experimental positions, we particularly encourage applicants with a strongrecord of accomplishments and interest in the development of new techniquesincluding applications of precision measurements to the abovementioned areas.For the theory positions, expertise in materials, biomolecular physics or optics isdesirable.Email abi.simsoniop.orgwww.brightrecruits.comThe Division has in place a broad cross disciplinary scheme with Materials Science,Engineering, Mathematical and Biological Sciences, and Chemistry, which isenhanced by an extensive infrastructure for the fabrication and sophisticatedcharacterization of materials.Applicants should also be, or show promise of becoming, excellent teachers at theundergraduate and graduate levels.Candidates should submit a curriculum vitae, publications list, research plan, andarrange to have three letters of reference sent to us. Electronic submissions arestrongly encouraged - use Subject: Faculty Search, and send to:PAPrecruit@ntu.edu.sg.et your obs noticed with oureatured recruiter option.Applications will be accepted until the positions are filled, but only those receivedby 1 Jul 2010 will be assured of full consideration. The appointment will begin on orafter 1 Jan 2011 depending on the circumstances of the successful applicant.Email chris.thomasiop.orgwww.brightrecruits.comPhD Position inUntitled-5 1 Theoretical Biological PhysicsCentre for Integrated19/4/10 10:50:40Systems BiologyImperial College LondonApplications are invited for a PhD position at Imperial College Londonto study the quantitative aspects of sensing and signalling in variousbiological contexts. Specifically, the role of cooperativity, feedback, noise,and cell mechanics in signal propagation and information processing will beinvestigated.For ideal candidate background and eligibility requirements, seehttp://www3.imperial.ac.uk/biologicalphysics/opportunities.Send application material to r.endres@imperial.ac.uket your obsnoticed with oureatured recruiteroption.Email abi.simsoniop.orgwww.brightrecruits.comPhysics World May 2010

sWork in a stimulatinginternational environmentwith the prospect ofpublishing in high-impactjournalsGross salary 27 k€,tax paid net salary>1550 €/month47-50 days of annualand compensatory leaveA lightfor scienceJoin the ESRFPh.D. Student Programme!Thesis subjects coverfrontline research in:physicschemistrybiologyESRFAll new positions onwww.synchrotronjobs.comor go towww.esrf.eu/jobsMAX PLANCK INSTITUTEMax-Planck Institute for the Science of LightGuenther-Scharowsky Str. 1/Bau 2491058 Erlangenhttp://mpl.mpg.defor the science of lightPrincipal Research FellowshipThe Max-Planck Institute for the Science of Light (Russell Division) is seekingoutstanding candidates for a Principal Research Fellowship (equivalent to a W2-level Associate Professorship). The successful applicant will have several yearspostdoctoral experience and an excellent track record in high-risk cutting-edgephotonics research. He/she will join a well-funded dynamic research group,based in extensive new laboratories, with many opportunities for national andinternational collaboration. As well as helping coordinate and advise a largeand enthusiastic team of PhD students, postdoctoral researchers and visitors,the appointee will be encouraged to develop his/her own research projects.Current research in the division focuses on scientific applications of photoniccrystal fibres, for example nonlinear optics and trapping in gas and vapour-filledhollow-core fibres (see www.pcfibre.com for more information). If desired,teaching opportunities may be arranged by agreement with the University ofErlangen-Nuremberg.The Max Planck Society is an equal opportunity employer. Applications fromwomen, disabled people and minority groups are particularly welcome.Full applications or informal enquiries should be sent by email to personal@mpl.mpg.de (postal applications will not be accepted). The closing date isJune 28, 2010, although late applications may also be considered. Max-PlanckInstitute for the Science of Light, Guenther-Scharowsky-Str. 1/Bau 24, D-91058Erlangen, Tel: +49-9131-6877-301.Lecturer (Two positions)Experimental Condensed Matter PhysicsSchool of PhysicsFaculty of ScienceJunior ScientistOPENINGonspatially resolved Raman spectroscopy● Leading international university● The Innovative Paul Scherrer and Institute creative is environmentwith 1300 employees the largest research centre for the● natural Clayton and campus engineering sciences in Switzerland and a worldwide leading user A two-year position, as a junior scientist, is available at the Istituto Officina dei Materialilaboratory. Its research activities are concentrated on the three main topics of solid-state of the Italian Council of Research on EU FP7 funded project aimed at performing RamanThephysics,Opportunityenergy and environmental research as well as human health.spectroscopy with nanometric spatial resolution.The School of Physics seeks to appoint two Lecturers (Level B), who will lead thedevelopment For the use of at innovative the beamlines research of programmes the Swiss Light in condensed Source (SLS) matter - one physics. of the mostThe successful candidate will have the opportunity to workApplicants advanced will radiation hold a PhD sources in an worldwide area relevant - the to Detector experimental Group condensed develops one- matter and twowithin the framework of an ambitious project funded by the EUphysics dimensional and have high a record speed of solid publications state detectors. and citations In a in collaboration the highest impact between physics the ESRFcommission which aims at the detection and identification ofjournals. (Grenoble, Successful France) applicants and PSI Eiger, will be a expected large multi to module attract single national photon competitive counting pixelsingle unknown molecules in biological systems. The idea isgrants, detector establish system an for independent applications research at synchrotrons, program, is being supervise developed. research studentsbased on atomic force microscope manipulation and extractionand contribute to undergraduate teaching. The capacity for scientific outreach andof molecules out of their specific environment and on theexperience In this respect, in engaging the SLS with Detector talented Group students is seeking would a be considered favourably.identification of the molecular composition through near-fieldFor more information about the School of Physics, go toRaman scattering spectroscopy. The selected scientist willhttp://www.physics.monash.edu.au/be in charge of the design and fabrication of new cantileversPostdoctoral FellowAll applications should address the selection criteria. Please refer to “How to Applyand of their implementation on a commercial AFM, in closefor Detector Monash jobs’ Development below.collaboration with the AFM manufacturer. She/He will also beSwiss Light Sourcedirectly involved in the use of the set-up for tip enhanced RamanThe Universityspectroscopy and microscopy. The scientist will benefit of a sideMonash University has a bold vision - to deliver significant improvements to theby side collaboration with the neurobiologists in charge of thehuman Your condition. tasks Distinguished by its international perspective, Monash takesbiological aspects and the physicist in charge of the opticalpride in Work its commitment on the development to innovative of the research pixel detector and high (optimization quality teaching of the and system,(spectroscopic, photonic and plasmonic) issues of the project.learning. performing measurements and data analysis)Eligible candidates must hold a PhD and a solid post-doc Implementation at beamlinesThe Benefitsexperience in biophysics and nanotechnology. A former Support of the detector systems and participation in X-ray experimentsRemuneration package: $84,614 - $100,479 pa Level B (includes employerexperience in scanning probe microscopy and/or design andsuperannuation Your profile of 17%).This role is a full-time position, however flexible workingdevelopment of microscopic and spectroscopic equipmentarrangements You hold a PhD may in be physics negotiated. preferably Monash in the field offers of silicon a range detector of professionaldevelopment. Youand/or microfabrication is strongly recommended. The position is for one year, renewable for adevelopment have good programs, knowledge support of analog for research, and digital study electronics and overseas and sensors work, generous for solid state second year, starting from September 2010. Yearly gross salary is €33,000, according to nationalmaternity detectors. leave Experience and flexible in work C/C++ arrangements. programming, data analysis and experience in regulations. Further informations are available at the following websites:Duration synchrotron Continuing radiation appointment instrumentation would be appreciated.http://www.cbm.fvg.it/laboratories/scanning_probehttp://www.singlemoleculedetection.eu/Location You will Clayton work as campus a team player in a stimulating international environment, giving you http://www.tasc.infm.it/~lazzarino/index.htmlEnquiries excellent Only opportunities for new initiatives and independent research.Interested applicants should submit a complete CV including list of publications and name of twoAssociate Professor Michael Morgan on +61 3 9905 3645 or email michael.referees (with e-mail address) by e-mail to:morgan@sci.monash.edu.auFor further information please contact: Dr Bernd Schmitt, phone +41 (0)56 310 23 14, Dr. Marco LazzarinoRef bernd.schmitt@psi.chNo A1010606IOM-CNR, Laboratorio TASC,Please submit your application to: Paul Scherrer Institut, Human Resources, Ref. codeApplications Close Friday, 2 July 2010Area Science Park, Basovizza, 34149 Trieste Italy6114, Elke Baumann, 5232 Villigen PSI, Switzerland or to: elke.baumann@psi.chlazzarino@tasc.infm.itApplications www.psi.chvia link belowphone: +39.040.375.6434http://monash.turborecruit.com.au/job/job_details.cfm?id=442421&from=fax: +39.040.226767Physics World May 2010 65

The Beilstein-Institut, located in Frankfurt am Main, is a leading, independent scientific foundation. An expanding programme of OpenAccess Journals is one of our major long-term projects. To add to our production team for our nanotechnology journal, we are currentlyseeking a full-timeScientific Editor (m/f)Responsibilities include:• Language editing and proofreading• Technical editing (editing and formatting of text and images) of scientific manuscripts• Production of html and PDF versions of articles• Support and monitoring of authorsQualifications required include:• Ph.D in physics, preferably nanotechnology, materials science or biophysics• Native English speaker; knowledge of German is desirable• Experience in scientific publishing an advantageWe offer a competitive salary with pension contributions and a good working environment as part of a highly motivated team.The ideal candidate will have excellent English and copyediting skills, good IT and online ability, a fundamental knowledge in scientificwriting and good knowledge of physics and nanotechnology.If you enjoy working as part of a team, have good communication skills and are able to work accurately and to deadlines, then pleasesend your letter of application, together with a full Curriculum Vitae and an indication of your salary requirements and when you would beavailable, to:Beilstein-Institut zur Foerderung der Chemischen WissenschaftenTrakehner Str. 7-960487 Frankfurt am MainGermanyE-Mail: jobs@beilstein-institut.deTo apply for this position, candidates must be eligible to live and work in Germany.For further information see www.beilstein-institut.de.Advertise your vacancy to a global audienceon the obs website from IOP Publishing.www.brightrecruits.com66Physics World May 2010

Home News Blog Multimedia In depth Jobs Events Buyer’s guideFor exclusivevideo interviewswith top laserscientists as partof our Laser at 50celebrations, go tophysicsworld.comAlso, check out our video seriesshowcasing laser science at theStanford Photonics Research CentreMultimediaMeredith LeeLife inside SPRC’sGinzton LaboratorySPRC executive directorTom Baer and colleaguestalk about the latest projectsand what life is like at the labOnline now...The first 50 years of the laser –and the next 50Tom BaerLasers in manufacturingAndreas TunnermannLasers in medicineBrian PogueLasers in spaceNarasimha PrasadLasers in optical communicationsTom HauskenMultimediaSteven BlockMultimediaPhil BucksbaumSingle-moleculebiophysicsFind out about thelaser-based optical tweezersunderpinning this pioneeringnew area of biologyProbing the ultrasmalland the ultrafastGet the low-down on theLinac Coherent Light Source(LCLS), the world’s brightestX-ray sourceFind all of these exclusives at physicsworld.com’s multimedia sectionphysicsworld.com

Lateral Thoughts: Captain Doctor Brunhilde Von Doom-Bootsphysicsworld.comA villain’s life in lasersI remember when lasers first made the papers. The re -search journals in the main dismissed them as a minorextension of previous work, but we in the InformalBrother hood of Supervillains recognized their potentialalmost straight away. After all, what is “light amplificationby stimulated emission of radiation” but the careful or -ganization of a corralled population into an untenablesituation, followed by a beam of high-energy, beefed-upphotons goose-stepping towards your target? The veryidea was too good to resist.So while scientists mocked lasers as “a solution lookingfor a problem”, we of the darker fraternity were workingon problems for those do-gooders to solve. I recall one ofthe earliest attempts, when my dear friend Blofeld wentfor the classic common-or-garden “city ransom” approach.He was never terribly original, poor chap, and I was almostglad when he was foiled by that Etonian thug, Bond. It leftthe rest of us free to pursue far more creative applications.And there was the other chappie – Gold-something-orother.He got all inspired by his time as a sous-chef in theOrient and decided that laser light would make the mostsublime secret-agent sushi. It was not an unstylish idea,even if in practice he had to downgrade his original laserscheme in favour of an oxy-acetylene torch and a flashlight.Technical difficulties, he said – but all in all it wasreally rather a good thing he ended up sparing Bond (himagain!), since the damned contraption would have maderather a mess of his lair.Of course, I was but a young stripling then. While theother kids were rocking round the clock, I was an aspir -ational, entry-level nemesis furtively pumping and pri -ming semiconductors in my dad’s shed. I still kept atransistor radio in my work area though, despite the dropin productivity – have you ever tried to air-cool a rubycrystal while distracted by thoughts of Keith Richards?He set me back weeks!But that moment – ah, that sweet moment when finelyunbalanced statistical energy distributions tumbled intoa perfectly coherent beam, putting Busby Berkeley toshame. I remember it like it was yesterday. The sweetozone smell of success was surpassed only by the joy ofdemanding the return of my Rolling Stones album in thebest way possible: by firing a tight phalanx of photons intothe neighbours’ begonias.So what if lasers were bulky? So what if they wereheinously inefficient? They had character. They had soul.I loved them, and if it was up to me, we in the Brotherhoodwould be menacing Lycra-clad men with them still. Butlike many things, superweapons have moved on. I guess Ishould not be surprised. Most of the soulful and personaltechnology from the last century is now regarded as somehowhilarious just because it was a bit chunky – a sentimentthat I am taking to heart increasingly as I age.But more to the point, maybe, perhaps the laser’sdemotion from its evil-weapon perch has come because itis no longer cutting-edge, obscure, inaccessible technology.CD players may retain a little yellow sticker saying“Danger – laser”, but no-one quivers at pieces of hi-fiequipment pointed in their general direction. Worse stillare the health applications. Poor Goldie’s freeze-driedcorpse would be turning in its orbit if he knew his in -dustrial cutting lasers were being used for humanitarian68I was anaspirational,entry-levelnemesisfurtivelypumping andprimingsemiconductorsin my dad’sshedpurposes. I mean, for Machiavelli’s sake, a significant proportionof the population even save up to have their eyesirradiated with our old superweapon! And that’s not evenincluding the more frivolous medical uses. One simplycannot wreak havoc with a dermatology tool. You mightas well menace people with an exfoliating pad.For a while, I tried incorporating lasers into other superweapons.Lasers on rods launched into active volcanoes;genetically engineered superwarriors who shoot laserbeams from their fingers; sharks with lasers à la my colleagueDr Evil; tidal-wave generators that would launchpods of shark-mounted lasers at coastal cities…after awhile it just got ridiculous. I had to accept the difficulttruth that lasers had been left behind, and I with them. Itwas time to retrain.These days, I am doing an Open University course ingenetics. Based on extensive readings of Nature, theDaily Mail and Michael Crichton, I gather that this is whatstrikes terror into the hearts of the modern populace. So,every weekend (and some evenings if there is time after myWomen’s Institute meeting), I go into my basement andtamper with nature. I am hoping to create a race of hypercoordinatedwasps that will infiltrate key governmentinstallations and hypnotize politicians with their synchronizedmovements and subtle frequency combinations. As afallback, I am also working on a bacterium that will subtlyruin the texture of any jam it comes into contact with, as Ifeel this would rapidly demoralize the nation – or at the veryleast win me the next WI preserve-making competition.It is hard work. Sometimes I feel the modern world ismoving too fast and I should settle down comfortablyinstead of trying to follow it. But in my heart, I know I willnever give up. Science is in my blood – or is that haemoglobin?– and it never rests. And neither can you youngwhippersnappers reading this, whether you are a “humanitarian”or one of our power-grabbing quango. You mightthink your shiny new nanotechnology is the bee’s knees,shark’s lasers or the sum total of every natural defence theplatypus can muster – but remember, today’s grey-goomediatedapocalypse is tomorrow’s run-of-the-mill nanomedicine.It can – and will – happen to you.Kate Oliver is a freelance science writer and author of theSchrödinger’s Kitten blog, e-mail thekitten@schrodingerskitten.co.ukPhysics World May 2010iStockphoto.com/RapidEye

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