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

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In the derivation for the optical density, it was assumed that the probe beam intensity I satisfies I ≪ Isat. Unfortunately this is not the regime with the best signal- to-noise ratio. The best signal-to-noise ratio is found for intensities I ≈ Isat. However, for a large enough number of atoms it is possible to achieve adequate signal-to-noise ratios even in the low-intensity regime. 7.5.2 Fluorescence Imaging and Calibration Fluorescence imaging of lithium atoms is very straight forward, and no special considerations have to be made. Even though fluorescence imaging is simple it is very useful for finding the image plane and calibrating the magnification of the imaging system. The image plane, and thus the position of the camera, can be found using a split-imaging technique. A mask with two or more holes is placed directly behind the imaging lens, as shown in figure 7.45. The fluorescence signal is then collected only through those two holes. If the camera is not placed in the image plane, the two images formed by the two spots will not overlap; they coincide only in the image plane. This method is a quick and easy way to locate the image plane. MOT object distance image distance Figure 7.45: Schematic setup for finding the imaging plane using a split-imaging technique. A mask with two or more holes is placed behind the imaging lens. The two images of the MOT coincide only in the imaging plane. CCD The magnification of an imaging system is typically determined by taking a series of images showing atoms in free fall. The center of mass position can then be used to calibrate the magnification. This method, however, has a couple of problems. Any 147
esidual potentials besides gravitation can lead to errors in the measured magnification. In addition, the determination of the center of mass of the atomic cloud is not always trivial, especially if the atoms are expanding as quickly as they do in a lithium MOT. A different method is therefore used in this experiment. A tightly collimated resonant laser beam (waist w0 ≪ 1 mm), traveling perpendicular to the imaging axis, is aligned to the center of the MOT. Atoms are loaded into the MOT. The MOT beams and the magnetic field gradients are then turned off so that the atoms expand. The resonant laser beam is pulsed and the fluorescent signal recorded. The laser beam is then translated vertically by a known amount, and a second image is taken. The fluorescence signal recorded by the camera moves by the same amount by which the laser was translated. Doing this measurement for multiple vertical positions, one can easily determine the magnification of the imaging system. 148
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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
Page 113 and 114: an ion gauge controller (Granville
Page 115 and 116: viewports (MDC, 450002) are attache
Page 117 and 118: not trapped by the MOT impinge on t
Page 119 and 120: Should contamination of the vacuum
Page 121 and 122: 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: = E0 1 −n2 √2 exp σ0 ± iE0
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 and 174: ubidium [113-115] and cesium[116].
Page 175 and 176: that most of the noise is due to th
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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