Experiments with Supersonic Beams as a Source of Cold Atoms

More documents

Recommendations

Info

described in section 3.3.1. While two of the coils failed in the course of the experiment, the remaining 18 coils are able to slow a supersonic beam of metastable neon from 461 m/s to 403 m/s. Importantly, the slowed beam is separated in time from the initial distribution, allowing it to be easily and clearly observed. 4.4.1 Beam Creation As noted above, the species slowed in this experiment is metastable neon. In its ground state electronic configuration, 1s 2 2s 2 2p 6 , neon has a closed shell structure and J = 0, making it insensitive to magnetic fields (except on the order of the nuclear magnetic moment which is ≈ 2000 times smaller than electronic magnetic moments). However, neon can be excited to the 1s 2 2s 2 2p 5 3s 1 configuration. The 3 P2 metastable state has a lifetime of 14.7 s [83], which is much longer than the few millisecond duration of these experiments. In the 3 P2 state, both mJ =1, 2 are low-field-seeking states, and since the Zeeman shift is directly proportional to mJ, itisthemJ = 2 sublevel which is targeted and slowed. The 3 P2 state has 5 magnetic sublevels, and atoms in the supersonic beam should be evenly distributed among these sublevels, at most 20% of metastable atoms in the beam are in the targeted state. There is also a 3 P0 metastable state in neon, which probably also makes up some percentage of the initial metastable beam. In the 3 P2 state, the Landé g-factor is 1.50 [84], which means that the magnetic moment of the atom is 3μB. The fine structure splitting of the states is around .05 eV and the magnetic field required to produce a shift of the same energy is around 300 T. Hence, the fields produced in these experiments are far lower than this, the Zeeman shift is the appropriate regime for any calculations. To give a sense of scale, the Zeeman shift at 1 T is .174 meV, and the kinetic energy of a metastable neon atom at 500 m/s is around 26 meV. Thus, fields of order several Tesla per stage are needed 75
nozzle front surface aluminum cathode stainless steel electrodes macor spacers (a) (b) (c) Figure 4.8: The discharge and discharge apparatus mounted to the valve are shown in these images. A CAD image of the discharge apparatus is shown in (a), and a photo of the assembled discharge apparatus mounted to the valve is shown in (b). A photo of the discharge is shown in (c). The bright source on the right side of this image is the filament, while the discharge is the red/purple glow between the discharge plates. to significantly change the energy of the beam. A pulsed DC discharge between a stainless steel plate and a hollow aluminum electrode is used to excite the neon atoms in the supersonic beam to the metastable state. The discharge apparatus is mounted to the front of the supersonic nozzle as seen in figure 4.8. The distance between the exit of the nozzle and the discharge region is 5 mm, which means that the beam is still under-expanded and quite dense, which improves the discharge efficiency. The discharge voltage is typically set at 1 kV and is pulsed for 3 μs. The pulse is produced using a Behlke HTS 31-03-GSM high voltage push-pull MOSFET switch, which gates a .112 μF high voltage capacitor bank. The current from the capacitor bank to the discharge is limited to 1 mA by a 1 kΩ resistor in series with the discharge. A filament biased at −100 V is mounted 2 cm from the discharge and 1 cm off the beam axis, which serves as an electron source that helps initiate and stabilize the discharge. The supersonic beam of neon in which the discharge is produced is created by the Even-Lavie supersonic nozzle described in chapter 2. Since neon is a noble gas, 76
Page 1 and 2:
Copyright by Adam Alexander Libson
Page 3 and 4:
General Methods of Controlling Atom
Page 5 and 6:
Acknowledgments First and foremost,
Page 7 and 8:
to problems, and I frequently went
Page 9 and 10:
General Methods of Controlling Atom
Page 11 and 12:
Table of Contents Acknowledgments v
Page 13 and 14:
Chapter 5. Towards Trapping and Coo
Page 15 and 16:
List of Figures 2.1 Comparison of e
Page 17 and 18:
5.12 Faraday Rotation Signal During
Page 19 and 20:
producing a cold sample. Alternativ
Page 21 and 22:
place inside a dilution refrigerato
Page 23 and 24:
atoms or molecules are slowed using
Page 25 and 26:
2.1 Thermodynamics of Ideal Gases F
Page 27 and 28:
Since there will be no heat exchang
Page 29 and 30:
Using equation 2.17 to modify equat
Page 31 and 32:
Normalized Effusive Beam Flux Norma
Page 33 and 34:
general method for producing cold a
Page 35 and 36:
The gas throughput of the nozzle ca
Page 37 and 38:
Chapter 3 Slowing Supersonic Beams
Page 39 and 40:
3.1 Using Helium for Atom Optics Ex
Page 41 and 42: Figure 3.1: Calculated elastic scat
Page 43 and 44: that they can be prepared ex-situ a
Page 45 and 46: successful. Any water that remains
Page 47 and 48: Skimmer 300 l/s Turbo Pump Even-Lav
Page 49 and 50: Figure 3.5: A CAD image of the dete
Page 51 and 52: from tubular aluminum welded togeth
Page 53 and 54: Figure 3.7: A CAD image of the roto
Page 55 and 56: Figure 3.10: A CAD image of large c
Page 57 and 58: Figure 3.11: This plot shows the am
Page 59 and 60: approximations are made in this cal
Page 61 and 62: 3.3.3 Detection An SRS [61] residua
Page 63 and 64: TTL pulse to the data acquisition c
Page 65 and 66: A comparison of the time-of-flight
Page 67 and 68: eceding crystal. Each curve is the
Page 69 and 70: calculated slow beam velocity is qu
Page 71 and 72: the RGA does have an effect on the
Page 73 and 74: Chapter 4 The Atomic and Molecular
Page 75 and 76: field. In the L − S coupling regi
Page 77 and 78: 3 P2 E Figure 4.2: This graph gives
Page 79 and 80: For intermediate fields, the full p
Page 81 and 82: Figure 4.4: This figure illustrates
Page 83 and 84: The same effect is also responsible
Page 85 and 86: (a) (b) (c) Time Figure 4.5: A pict
Page 87 and 88: which the particles enter). The oth
Page 89 and 90: the coil can instead be switched be
Page 91: the magnitude of the field some dis
Page 95 and 96: Figure 4.9: A CAD overview of the s
Page 97 and 98: 258V 1MΩ 5V 1mF DC/DC Converter TT
Page 99 and 100: Figure 4.12: An oscilloscope trace
Page 101 and 102: (a) (b) Figure 4.14: A CAD image of
Page 103 and 104: -HV PS 4 M MCP Anode 10 M 1 M Trans
Page 105 and 106: Signal [V] 2.5 2.0 1.5 1.0 0.5 refe
Page 107 and 108: Figure 4.20: An exploded view of th
Page 109 and 110: (a) (b) (c) (e) Figure 4.21: A pict
Page 111 and 112: 258V 1MΩ TTL 2.2mF 50Ω TTL 5V 5V
Page 113 and 114: closed. With the new thyristor gate
Page 115 and 116: HeNe M2 M1 BB /2 L BB PC coil PC PD
Page 117 and 118: Table 4.1: Peak magnetic fields mea
Page 119 and 120: Figure 4.28: A cut-away CAD image o
Page 121 and 122: ameters. The coilgun chamber consis
Page 123 and 124: Table 4.2: Final velocities (vf), s
Page 125 and 126: MCP Signal [arb. units] 2.0 1.5 (1)
Page 127 and 128: viability for molecules essential.
Page 129 and 130: 8 Ω LN2 Liquid Nitrogen Dewar Nozz
Page 131 and 132: Figure 4.33: Molecular oxygen slowi
Page 133 and 134: Chapter 5 Towards Trapping and Cool
Page 135 and 136: Energy meV 0.05 0.00 0.05 0.0 0.2 0
Page 137 and 138: 10 mm 2.0 T 1.8 1.6 1.4 1.2 1.0 0.8
Page 139 and 140: 250V 1MΩ 3x 2.2mF TTL 5V feedback
Page 141 and 142: Magnetic Field (T) 1.9 1.7 1.5 1.3
Page 143 and 144:
5.2.2.1 Principle of Operation of t
Page 145 and 146:
Figure 5.8: Photograph of the trapp
Page 147 and 148:
4.1.3. In an anti-Helmholtz trap, t
Page 149 and 150:
Figure 5.11: Photograph of the hydr
Page 151 and 152:
Photodiode Signal (V) Time (s) Figu
Page 153 and 154:
Figure 5.13: Time of flight plot of
Page 155 and 156:
500 l/s Turbo Pump Supersonic Nozzl
Page 157 and 158:
Ionizer 500 l/s Turbo Pump Ion Opti
Page 159 and 160:
guided the design of the apparatus.
Page 161 and 162:
Z − Velocity (m/s) 100 60 30 0
Page 163 and 164:
Atom Number 60 50 40 30 20 10 0.6 0
Page 165 and 166:
scattered photon to extract informa
Page 167 and 168:
where k1 · pi = − k2 · pi, wh
Page 169 and 170:
the electron g-factor which causes
Page 171 and 172:
Figure 5.24: A schematic of the tel
Page 173 and 174:
prevent the determination of the is
Page 175 and 176:
(a) (b) time Figure 5.25: A 1D illu
Page 177 and 178:
experiment, where a being is capabl
Page 179 and 180:
potential position 2 x 243 nm Lα |
Page 181 and 182:
Appendix 164
Page 183 and 184:
y x V i Figure A.1: The geometry us
Page 185 and 186:
Bibliography [1] H.J.MetcalfandP.va
Page 187 and 188:
[17] Brian C. Sawyer, Benjamin L. L
Page 189 and 190:
[34] R. Campargue. Progress in over
Page 191 and 192:
[51] O. Carnal, M. Sigel, T. Sleato
Page 193 and 194:
[70] Edvardas Narevicius, Adam Libs
Page 195 and 196:
[87] Willis E. Lamb and Robert C. R
Page 197 and 198:
[96] G.Gabrielse,N.S.Bowden,P.Oxley
Page 199 and 200:
[110] N. Kolachevsky, J. Alnis, S.
Page 201 and 202:
[125] Andreas Osterwalder, Samuel A
Page 203 and 204:
[142] C. Cohen-Tannoudji, B. Diu, a
Page 205 and 206:
[161] Paulo F. Bedaque, Aurel Bulga
show all

Experiments with Supersonic Beams as a Source of Cold Atoms

Create successful ePaper yourself

Delete template?

Save as template?