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

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heat sink allow for the connection of current connectors to the coil without establishing an electrical connection between the current supply and the heat sink. (a) (b) Figure 7.20: Feshbach coil heat sink. (a) A small gap in the heat sink reduces eddy currents. The inside is hollow so that water can remove resistive heat from the coils. (b) The current connectors are attached to the Feshbach coil (orange), without establishing an electric contact between the current supply and the heat shink. The current connectors are soldered to the coil with Indium solder (Indium Cor- poration of America, alloy 58Bi 42Sn). This epoxy has a lower electrical resistance than regular solder and a lower melting point (138 ◦ C). Both the coil and the copper current connectors have a large volume of copper that need to be heated, and it is impossible to directly solder the current connector to the coil. Standard soldering irons are not able to produce enough heat, even with the reduced melting point of the solder. The Feshbach coil with the heat sink connected is therefore heated to 130 ◦ C using heater tape. The current connectors are heated separately in the oven typically used for curing of epoxy. With both coil and connector close to the melting point temperature of the solder the electrical connection can be made with a standard soldering iron. Before attaching the two pieces together, diamond filled epoxy is applied to the indentation of the heat sink. This stabilizes the current connector to the heat sink and provides a large resistivity between the two parts. To further support the weight of the current connectors, epoxy putty (Loctite, Fixmaster underwater repair epoxy) is used to create another mechanical support between the current connectors and the heat sink. 111
The coils are then checked for shorts and the resistance of the coils and the heating of the coils is measured. The resistance is approximately 0.03 Ω. Figure 7.21 shows the temporal evolution of the temperature for different currents. The steady state temperature remains below 70 ◦ C even at a current of 150 A (B ≈ 951 G). The water flow through the heat sink is between 2.1 and 2.4 l/min, and the water temperature is set to 18 ◦ C. High currents in the Feshbach coils are only required during the evaporation stage of the experiment. It is therefore estimated that during the experiment the steady state temperature will not exceed 35 ◦ C. Figure 7.21: Temperature increase in the Feshbach coils at several current values. The current to the Feshbach coils is provided by a Lambda power supply (ESS 20-500). This power supply is able to provide up to 500 A of current at 20 V, and the current is stabilized to within 0.1%. In addition to running the coils in Helmholtz configuration during evaporation, they can also operate in anti-Helmholtz configuration. This is achieved by an H-bridge setup built from a group of MOSFETs. The MOSFET setup with water-cooling is shown in figure 7.22. Each MOSFET (IRF1324PbF) can in principle take a current of 195 A. However, the maximum current is limited by the quality of the connections as well. A 112
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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
Page 77 and 78: 4.3.1.4 Upper MOT Horizontal Slave
Page 79 and 80: provides the beam for the upper MOT
Page 81 and 82: demon beam λ λ horizontal MOT bea
Page 83 and 84: scholar, Florian Schreck. It is wri
Page 85 and 86: Atoms are then optically pumped to
Page 87 and 88: ferred into the |F = 1,mF = 0〉 or
Page 89 and 90: 5.2 Branching Ratios and Population
Page 91 and 92: effect of the reflected beam at zer
Page 93 and 94: y the repulsive trough beams, gaini
Page 95 and 96: Figure 5.9: Atom number as a functi
Page 97 and 98: Figure 5.10: Radius of the magnetic
Page 99 and 100: on the collision rate of atoms insi
Page 101 and 102: ferred via the single-photon coolin
Page 103 and 104: By comparison an atomic Fock state
Page 105 and 106: of atoms in the two hyperfine groun
Page 107 and 108: difference in the lifetimes is dete
Page 109 and 110: Chapter 7 Lithium Apparatus Creatin
Page 111 and 112: 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
Page 125 and 126: BGauss 250 200 150 100 50 30 20 10
Page 127: are required to create the high mag
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 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)
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Figure 8.11: Different shapes of MO
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ZnSe lens f=5 in knife edge ZnSe wi
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shown in figure 8.13. By matching t
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Figure 8.15: Atom number and temper
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275 Hz. Using these values the beam
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system. Maybe the easiest way to ac
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Appendix A Magic Wavelength of Hydr
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transitions for the excited state p
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Bibliography [1] J.J. Thomson. Cath
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[22] C.J. Foot. Atomic Physics. Oxf
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[46] E.D. Black. An introduction to
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[67] J.L. Hanssen. Controlling Atom
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[88] D.S. Naik, C.G. Peterson, A.G.
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[110] J.W. Goodman. Introduction to
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[132] C. Degenhardt, H. Stoehr, U.
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