Experiments to Control Atom Number and Phase-Space Density in ...

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MOT beams MOT Mirror M1 APD 2 CO 2 beam Lens L1 Lens L3 MOT image D-shaped mirror M2 x y Lens L2 z APD 1 Figure 8.8: Experimental setup for locating the CO2 laser beam within the trapped cloud of MOT atoms. The three pairs of retro-reflected MOT beams excite fluorescence in the atoms of the MOT. The CO2 beam is located in the general vicinity of the trapped cloud of atoms. The mirror M1 reflects the fluorescence light from the MOT. The lens L1 collects the fluorescence light and creates an image of the MOT. In the image plane a D-shaped mirror (M2) cuts the fluorescent signal into two halves. These are individually focused by two lenses (L2 and L3) onto two avalanche photodiodes (APD1 and APD2). the optical access that is available to collect the fluorescence light. Ideally the collection angle is maximized to capture a large number of scattered photons from the MOT atoms. Particular care is taken to reduce any scattered light from the MOT beams as much as possible in order to optimize the signal to noise ratio. In the image plane of the lens L1 the signal of the MOT is split 50:50 in the vertical dimension. The light is then collected with two f = 25 mm lenses (L2 and L3) and focused onto two avalanche photodiodes (APDs). To do balanced detection the signals of the two APDs are substracted from each other. Figure 8.9 shows the measured noise spectra of (a) the electronic noise in combi- nation with the noise caused by scattered light without atoms trapped in the MOT and (b) the noise of the system with atoms trapped in the MOT. These spectra clearly show 157
that most of the noise is due to the scattering of photons from the atoms. Most of the noise occurs at frequencies below 2 kHz. This is explained by the timescales with which the atoms move within the capture volume of the MOT. (a) (b) Figure 8.9: (a) Electronic noise and noise caused by scattered light. (b) Noise Spectrum in the presence of the MOT. In both cases the signal of the two APDs are substracted and the difference is recorded. At this point it is possible to start the balanced lock-in detection. The CO2 laser is pulsed at a frequency f1 by turning the AOM on and off using an RF switch. The presence of the CO2 laser beam slightly changes the spatial distribution of the atoms within the MOT, causing a slight imbalance in the previously balanced signal from the APDs. Because this change is very small lock-in detection at the frequency f1 is used to filter the small signal out of the large background noise. The ideal pulsing frequency is in principle determined by three factors: the electronic noise in the APDs and the lock-in amplifier, which can be neglected in this case, the noise caused by fluctuations in the MOT, and the timescale at which the atoms will be able to react to the presence of the CO2 laser beam. The ideal pulsing frequency is determined to be around 2.4 kHz. Figure 8.10 (a) shows a sketch of how the coordinate system at the lens used to focus the CO2 laser into the vacuum chamber is seen at the image location of the MOT. The horizontal black line indicates where the signal of the MOT is split into the two separate halves. z is the propagation axis of the laser beam and passes through the 158
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Copyright by Kirsten Viering 2012
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Experiments to Control Atom Number
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Acknowledgments First of all, I wou
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Experiments to Control Atom Number
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Table of Contents Acknowledgments v
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Chapter 7. Lithium Apparatus 92 7.1
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List of Tables 2.1 Physical propert
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4.1 Vacuum chamber . . . . . . . .
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7.39 Future vertical axis optics .
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The development of techniques to la
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Ptorr 10 5 10 6 10 7 10 8 10 9 260
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Property Symbol Value Reference Ato
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2.3.2 Hyperfine Structure So far th
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The Wigner-Eckhart theorem can be u
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The total magnetic moment of an ato
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interaction. The shift in the energ
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(a) (b) scattering length a 0 Energ
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a laser field with frequency ω. Th
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Here ω0 is the resonance frequency
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Optical molasses do not provide a s
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J=1 J=0 -1 Δ σ + σ - σ - 0 +1 -
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phase-space density is defined as
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which maintains a constant η = U/k
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2.12.1 Saturated Absorption Spectro
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Figure 2.22: Saturation absorption
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Signal 0 Signal (a) (b) Signal Freq
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(a) (b) (c) (d) Figure 2.24: Absorp
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y more complex energy level structu
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ight side of the box. An irreversib
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time (a) (b) (c) Figure 3.3: Single
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them to move from B to A, but close
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Figure 4.1: Vacuum chamber. Photogr
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( ( Figure 4.3: Helicoflex seal. (a
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88 mm 4.2.3 Auxiliary Coils 62 mm Q
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5 2 P 3/2 5 2 S 1/2 384. 230 484 46
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distribution of the MOT master lase
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shifts. First a frequency shift of
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transition. However, the laser freq
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4.3.1.4 Upper MOT Horizontal Slave
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provides the beam for the upper MOT
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demon beam λ λ horizontal MOT bea
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scholar, Florian Schreck. It is wri
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Atoms are then optically pumped to
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ferred into the |F = 1,mF = 0〉 or
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5.2 Branching Ratios and Population
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effect of the reflected beam at zer
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y the repulsive trough beams, gaini
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Figure 5.9: Atom number as a functi
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Figure 5.10: Radius of the magnetic
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on the collision rate of atoms insi
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ferred via the single-photon coolin
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By comparison an atomic Fock state
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of atoms in the two hyperfine groun
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difference in the lifetimes is dete
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Chapter 7 Lithium Apparatus Creatin
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angle valve rotary feedthrough ion
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an ion gauge controller (Granville
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viewports (MDC, 450002) are attache
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not trapped by the MOT impinge on t
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Should contamination of the vacuum
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Figure 7.12: The assembled Zeeman s
Page 123 and 124: 7.2.2 MOT Coils A second set of coi
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Page 127 and 128: are required to create the high mag
Page 129 and 130: The coils are then checked for shor
Page 131 and 132: + B A Figure 7.23: Feshbach coil H-
Page 133 and 134: ensure that no particulates build u
Page 135 and 136: 118 Figure 7.26: Optical layout of
Page 137 and 138: The error signal shows three lines,
Page 139 and 140: into the CO2 laser. The optical lay
Page 141 and 142: Thorlabs PDA10A Coupler ZDC-10-1 to
Page 143 and 144: Imaging ber Imaging ber from Imagin
Page 145 and 146: Table 7.4 summarizes the beam power
Page 147 and 148: CO2 laser 40 MHz AOM f=2 in f=2 in
Page 149 and 150: 132 Figure 7.38: Optical layout aro
Page 151 and 152: Feshbach coil objective lenses atom
Page 153 and 154: MOT beams are no longer traveling a
Page 155 and 156: The second card (NI6733) offers eig
Page 157 and 158: Averaging over the magnetic subleve
Page 159 and 160: 2 2 P 3/2 D 2=670.977nm 2 2 S 1/2 m
Page 161 and 162: The right hand side of equation 7.1
Page 163 and 164: = E0 1 −n2 √2 exp σ0 ± iE0
Page 165 and 166: esidual potentials besides gravitat
Page 167 and 168: Figure 8.1: MOT loading. Typical lo
Page 169 and 170: A linear ramp typically changes the
Page 171 and 172: A typical MOT is density-limited at
Page 173: ubidium [113-115] and cesium[116].
Page 177 and 178: (a) (c) y . x z X=0.0mm Z=2.5mm 1)
Page 179 and 180: Figure 8.11: Different shapes of MO
Page 181 and 182: ZnSe lens f=5 in knife edge ZnSe wi
Page 183 and 184: shown in figure 8.13. By matching t
Page 185 and 186: Figure 8.15: Atom number and temper
Page 187 and 188: 275 Hz. Using these values the beam
Page 189 and 190: system. Maybe the easiest way to ac
Page 191 and 192: Appendix A Magic Wavelength of Hydr
Page 193 and 194: transitions for the excited state p
Page 195 and 196: Bibliography [1] J.J. Thomson. Cath
Page 197 and 198: [22] C.J. Foot. Atomic Physics. Oxf
Page 199 and 200: [46] E.D. Black. An introduction to
Page 201 and 202: [67] J.L. Hanssen. Controlling Atom
Page 203 and 204: [88] D.S. Naik, C.G. Peterson, A.G.
Page 205 and 206: [110] J.W. Goodman. Introduction to
Page 207: [132] C. Degenhardt, H. Stoehr, U.
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