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

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ization of the beam. The second cube reflects a fixed amount of power. Fluctuations in this power can be measured with the photodiode and fed back to an AOM used to stabilize the power. 7.4 Computer Control and Data Acquisition The computer control and data acquisition software and hardware is an updated version of the rubidium system. A newer version of Control, a Visual C++ program originally written by Florian Schreck, a former postdoctoral scholar, offers precision timing of 500 ns of the experimental sequence, and a user-friendly graphical interface. Control communicates with three different National Instruments cards, NI6533, NI6733 and NI PCI-GPIB. It generates a waveform of the experimental sequence and sends the infromation as 25 bit data to the NI cards. The first 16 bits are used for data, the next 8 address the different outputs and the last bit is used as a strobe bit to synchronize the outputs. This is necessary to achieve a timing precision of 500 ns. All 25 bits from Control are sent to all of the outputs, however, only the one with the matching address will respond. The first of the NI cards (NI6533) controls 16 analog outs, 32 digital outs and 9 direct digital synthesizer (DDS) boards. The output from the NI card first goes to a bus driver/buffer card. Here the signal is amplified and connected to flat ribbon cables, that connect to the home-built digital/analog out cards and the DDS. The analog and digital out cards from the rubidium experiment have to be modified to allow for the increased timing precision. The design of these boards can be found at [108]. The setup currently has two analog out cards, each with 8 channels per board, and two digital out cards with 16 digital outs each. The analog boards provide an output voltage between −10 V and +10 V, the digital outs work as TTL signals with a high of around 3.5 V. In addition 9 DDS boards are currently installed. These are based on the AD9852 DDS IC and provide frequencies up to 135 MHz. A commercial frequency generator (Wavetek 2407) provides a 300 MHz reference signal to the DDS boards. The DDS are used as frequency sources for the AOMs. 137
The second card (NI6733) offers eight digital in/out and two 24 bit counters. This card will be used for acquiring single atom detection data. For each detected photon the avalanche photodiode (APD) generates a pulse. These pulses can then be counted with the help of this card. The last card (NI PCI-GPIB) is able to control GPIB-cabale devices and is used to interface with GPIB devices. Thus far it was mainly used to communicate with an arbitrary function generator (Agilent 33250A). A second PC runs a program called Apogee Server. This program controls the two cameras in the experimental setup: The USB camera Apogee Alta U47+ and the FireWire camera Stingray F033B/C from Allied Vision Technologies. A third computer, running the software Vision, also written by Florian Schreck, communicates both with Control and Apogee Server. If a picture is to be taken during the experimental sequence, Control sends this information to Vision, which in turn tells Apogee Server to prepare the camera. Control then triggers the camera and Apogee Server downloads the picture information from the camera and sends the data to Vision. The main purpose of Vision is data evaluation. Depending on the type of image taken, Vision automatically displays the fluorescence image, or uses the raw absorption, the probe, and the noise image of absorption imaging to calculate the optical density. It also fits the data to determine atom number, the spatial extent of the cloud, etc. Vision automatically stores all the images and all the variables with values used in the experimental sequence. This allows a complete reconstruction of the experimental sequence at any time. 7.5 Imaging Imaging of lithium atoms using absorption imaging techniques is more compli- cated than for rubidium, due to the differences in energy level structure. Corrections to the simple formulas given before are therefore required. In addition it can be very helpful to image the atoms at a homogeneous magnetic field, and the presence of the field has to be taken into account during the imaging process. 138
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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
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 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: MOT beams are no longer traveling a
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)
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.
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[110] J.W. Goodman. Introduction to
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[132] C. Degenhardt, H. Stoehr, U.
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