Orbital Angular Momentum in Radio Experiments - Swedish Institute ...

15 th annual RF Ionospheric Interactions Workshop, Boulder, 19 April, 2009
Orbital Angular Momentum in Radio Experiments
New ways to observe and excite plasma vorticity
Bo Thidé
Swedish Institute of Space Physics, IRF, Uppsala, Sweden
LOIS Space Centre, Växjö, Sweden
with contributions from the LOIS OAM/radio topology collaboration
J. Bergman, L. Daldorff, S. Mohammadi, T. Leyser, E. Nordblad. L. Norin (Uppsala),
R. Karlsson (Graz), T. Carozzi (Glasgow), H. Lundstedt (Lund), W. Löwe, W. Baan, M. Milrad (Växjö),
M. Fredriksson, N. Ibragimov, R. Khamitova. C. Svahnberg (BTH, Karlskrona),
H. Then (Oldenburg), T. Mendonca (Lisbon), Ya. N. Istomin (Lebedev Institute, Moscow),
E. Weibust, B. Sjökvist (IBM Sweden), B. Elmegreen, L. Amini, A. Biem, D. Turaga,
and O. Verscheure (IBM Research, NY)

SEE as an on-demand space plasma EM
turbulence diagnostics
Complements – and supplements – optics, radars, satellites,etc.
BoThidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Secondary HF radio emission dependence
on primary HF radio frequency ce
HF pump frequency swept continuously up and down across 4f at Sura, Russia
BUM hysteresis
HF excited secondary radiation (SEE) as recorded at the radio facility SURA near Nizhniy Novgorod,
Russia, 1999. The HF pump frequency is swept across the ionospheric 4 th electron gyroharmonic.
Pump
60 kHz
(Click for animation)
4f
5340 kHz ce
5540 kHz
BoThidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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First detection of angular momentum in SEE
Experiments at HEATING, Tromsø, 1983
Bo Thidé. Stimulated Electromagnetic Emission and nonlinear wave-wave interactions in
ionospheric heating experiments. In M. Q. Tran and M. L. Sawley, editors, Proceedings,
Contributed Papers, International Conference on Plasma Physics, volume I, page 131,
Lausanne, Switzerland, 27 June-3 July 1984. Centre de Recherche en Physique des
Plasmas, Ecole Polytechnique Federal de Lausanne, CRPP-EPFL.
Circular, (nearly) O-mode pumping
O mode SEE
X mode SEE
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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First full polarimetry studies of SEE
Experiments at SURA,Vasil’sursk, September 1998
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Lorentz’s microscopic Maxwell equations
for the EM field (1903)
Symmetric under inhomogeneous Lorentz transformations. The concomitant Lie
group is the 10-dimensional Poincaré group P(10). According to Noether’s
theorem there therefore exist 10 conserved EM quantities. In fact there are 25
exact continuous symmetries/conserved quantities (in vacuo), plus an as yet
unknown number of approximate, conservation laws [Ibragimov, 2008].
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Conserved quantities in a closed electromechanical
system (matter + EM fields) [Boyer, 2005] (1)
Homogeneity in time => conservation of system energy
(no EMF, no radiation; cf. Poynting’s theorem):
Homogeneity in space => conservation of system linear
momentum (gives, e.g., rise to EM Doppler shift):
Foundation of conventional ‘linear momentum’ radio.
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Conserved quantities in a closed electromechanical
system (matter + EM fields) [Boyer, 2005] (2)
Invariance under proper Lorentz transformations =>
conservation of system centre of energy:
Isotropy in space => conservation of system angular
momentum (gives rise to azimuthal Doppler shift):
The first part is the mechanical angular momentum J mech .
The second part is the EM angular momentum J em .
Foundation of ‘angular momentum’ radio or ‘dual radio’.
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Total EM field angular momentum
For radiation beams in free space, EM field angular momentum J em can
be separated into two parts (for x 0 = 0) [Jackson, 1998; Thidé, 2009]:
For each single Fourier mode in real-valued representation [van Enk &
Nienhuis, 1992]:
The first part is the EM spin angular momentum (SAM) S em , a.k.a. wave
polarisation, and the second part is the EM orbital angular momentum
(OAM) L em .
NB: In general, both EM linear momentum p em , and EM angular
momentum J em = L em + S em are radiated all the way out to the far zone!
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Standard textbooks show that classical
EM angular momentum is radiated
all the way to infinity
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Difference between polarisation (SAM) and orbital
angular momentum (OAM)
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Micromechanical action of SAM and OAM
Particles of sizes 1–3 μm irradiated by SAM/OAM laser beams
Spin angular momentum s = 1 Orbital angular momentum l = 8
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Challenge: Ionospheric and atmospheric turbulence
distort low-frequency radio signals from outer space
Today it is possible to compensate (‘self-calibrate’) for amplitude and nonsingular
phase distortion of signals propagation through the ionosphere. Data
from observations at VLA (Very Large Array, NM, USA) at 74 MHz.
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Phase singularities (dislocations) are to be expected
in radio beams propagating through space
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Imparting OAM onto an EM beam (laser, mm wave)
with the help of a spiral plate or hologram
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Prediction: Ionospheric and other space plasma
turbulence can change the topology of radio signals
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Plasma vorticity couples to radio
OAM => topological distortion
PRL
NPG
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Nonlinear excitation of OAM in plasma
PRL, in press
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Even neutrino beams can be endowed with OAM!
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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EM beam with circular polarisation (SAM) S but
no orbital angular momentum (POAM) L
Phase fronts (loci of constant phase)
Optics (LG)
Radio
M. J. Padgett, J. Leach et al., U. Glasgow, UK; Royal Society
Sjöholm and Palmer, 2007
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Instantaneous field vectors across an antenna
array for a radio beam with circular SAM
Phase 0 deg
Phase 45 deg
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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EM beams on the same frequency but with different OAM
would be orthogonal and not interfere with each other
Spiraling Poynting/linear momentum (and OAM) vectors!
l=+1
l=+3
l= -4
Bo Thidé 22

Instantaneous field vectors in a cross section of
a radio beam carrying both SAM and OAM
Phase 0 deg
Phase 45 deg
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Three orthogonal dipole antennas sample E(t,x)
Three orthogonal loop antennas sample B(t,x)
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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3D vector antennas allow new types of diagnostics
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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LOIS radio idea: Sample the entire field vectors in
time and space (LOIS stn true superset of LOFAR stn)
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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LOIS resources 2003–today (total ~ 2.5 MEur)
Computer cluster (two SUR grants from IBM),
currently in Uppsala. To be moved to Ronneby
The control room at the LOIS Test Station Risinge/Växjö.
Radio Sweden’s 500 kW transmitter located about
100 km south of the Växjö LOIS test station and
100 km south-west of the Ronneby prototype
station site. Will be used for space radar tests.
9m×8m×6m antenna chamber,
Ångström Lab, Uppsala
Magnetometer, LOIS Test
Station, Risinge/Växjö
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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LOIS prototype station under construction in Ronneby
To be augmented by two outer, concentric rings, with 16 and 32 radio units,
respectively, for a total of 56 units with three dipoles each (funding permitting)
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Mechanical effects of EM orbital angular momentum
(OAM) predicted 1992
Beth’s experiment, 1936
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Radio beams from circular antenna arrays
can be made to carry OAM!
Thidé et al., Phys. Rev. Lett., 99, 087701, 2007
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Field vector sensing means total configurability
Very good solar radio coronagraph!
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Radio beam topology degrees of freedom
Conventional linear momentum (Poynting) flux and E
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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The radio results agree with EM OAM theory
Theory predicts that a circular polarised radio beam in a pure
OAM eigenstate with azimuthal phase dependence exp(ilφ),
frequency ω, and energy H, should have a total angular
momentum component J z
EM
= lH/ω along the z (beam) axis.
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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LOIS prototype station sensitivity
48 tripoles=144 dipoles
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Very readable paper on POAM in astrophysics
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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POAM in astronomy – A very recent and very
comprehensive treatise
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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2D LOFAR/SKA-type interferometers exhibit
polarisation aberration. 3D interferometers do not
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Europe is leading the way
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Observations at 94 GHz of angular momentum
induced azimuthal (rotational ) Doppler shift
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Rotational Doppler shift spectrum
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Deep space radar requirements
From Paul Rodriguez
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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OAM spectrum probing (spiral imaging) – a
new radar diagnostic
Recent digital spiral imaging experiments (Ll. Torner et al., Opt. Express, 13, 873–881, 2005;
Molina-Terriza et al., J. Eur. Opt. Soc., Rapid Publ., 2, 07014, 2007) have demonstrated that
probing with OAM gives a wealth of new information about the object under study.
The stimulus…
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Spiral (OAM) spectrum imaging results
…and its response
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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OAM detection of inhomogeneities (in transmission)
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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EM vorticity/OAM as turbulence diagnostic
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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OAM makes a new (spiral) frequency Ω available
Interesting consequences for radio communications
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Single photons can carry both spin angular
momentum S and orbital angular momentum L!
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Pack EM beams with much more data by
utilising more topological degrees of freedom
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Hyperentangled SAM and OAM photon states break
the linear-optics channel capacity threshold
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Shannon’s law revisited
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Photon OAM for observing black holes?
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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New ideas – new audiences. SETI?
‘…The investigation of new
transmission modes by Thidé and
Bergman hints that if we do find a
signal from ET, we may wish to
reconfigure our radio telescopes to
look for encoding of the message via
such subtle effects as orbital angular
momentum. A simple signal may only
be a cipher for a more complex
message, and there may be more
things in heaven and earth than even
Maxwell had dreamt of …’
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Conclusions
• Using all ‘degrees of freedom’ (conserved quantities)
allows full characterization and extraction of all
information carried by beams of EM waves/photons
• Has already provided better diagnostics in laser
physics and is entering free-space communications
• Can use conventional radio techniques to apply these
new results to the radio domain
• The radio domain results hold great promise for new
fundamental optics and improved remote diagnostics
• World’s first (?) OAM radio laboratory at Ångström
Lab, Uppsala, is now coming on line
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Thank you for your attention
....there may be more things in heaven and earth than even Maxwell had dreamt of …
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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New ideas – detection of magnetic monopoles by
measuring the symmetry properties of the EM field?
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Radiation of power/linear momentum vs.
radiation of angular momentum
Outside (but not inside) the source
region, the fields can be accurately
approximated by an expansion in
spherical waves:
The approximation (2) of approximation (1) is
excellent for radiation of linear momentum
(power, Poynting flux) but is completely
wrong for radiation of angular momentum.
The E R term excluded is the only term which
gives rise to radiation of angular momentum!
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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That far-zone POAM is generated by near-zone
longitudinal E fields is well known since 1914
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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Spin-off LOIS developments for space physics,
astroparticle physics, and space communications
Vector sensing radio on a chip, 33×33 mm 2
at 4 grammes based on bare die
components on silicon
Vector radio system for detection of
UHE neutrino induced radio pulses in
the Antarctic ice
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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LOIS physics idea: Space physics, space weather,
solar radar, ionospheric turbulence ...
Download from www.lois-space.net
Bo Thidé 15th annual RF Ionospheric Interactions Workshop, Boulder, 20 April, 2009
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