Experiments with Supersonic Beams as a Source of Cold Atoms

More documents

Recommendations

Info

actually a transverse rather than longitudinal effect. With so many coils, the beam can be brought to low velocity using small phase angles. While the beam is still moving quickly the atoms propagate well into the coil before it is completely off, allowing the focusing and transverse guiding properties of the field inside the coil to provide transverse stability. However, by continuing to use a large phase even when the atoms are slow, they do not get into the coil before the field is off. This means that the antiguiding force applied outside of the coil dominates and the atoms are de-focused, leading to a loss of flux as atoms hit the walls of the coilgun and are lost. The metastable neon beam is not slowed below 55.8 m/s because the beam flux decreases rapidly for lower velocities. Looking at how the flux decreases at both the extended and retracted positions of the MCP shows that the decrease in flux is primarily due to the transverse velocity of the atoms in the beam. However, this velocity is sufficient for most purposes, since the beam is slow enough that it could be loaded into a stationary magnetic trap. 4.6 The Molecular Coilgun: Stopping Molecular Oxygen Having shown that the coilgun method gives full control of the velocity of a beam of atoms, the next step is to show the generality of the coilgun method. Slow- ing of metastable neon demonstrates control over atomic velocities, but slowing of a molecule demonstrates the broad applicability of the coilgun method, and shows that it is a general method of producing cold and slow samples. To this end, the coilgun is used to slow a beam of molecular oxygen. Oxygen is chosen because it has a permanent magnetic moment in the ground electronic state, and because of its importance in several chemical processes. Being a molecule, oxygen has a more com- plicated internal energy level structure with avoided level crossings between different rotational states. This makes an experimental demonstration of the coilgun method’s 109
viability for molecules essential. In the experiment described here, oxygen is slowed from an initial velocity of 389 m/s to a 83 m/s, removing more than 95% of the initial kinetic energy. The apparatus used for this is almost identical to the apparatus used to stop metastable neon, and the coilgun used is exactly the same. As such, only the differences between the experiments (in beam creation and detection) are discussed. 4.6.1 Oxygen’s Magnetic Levels At this point, it is useful to consider how the rotational spin states of oxygen affect its interaction with a magnetic field. The state that is slowed is the 3 Σ − g ground state. Nuclear statistics forbid the existence of K =0, 2, 4,...rotational levels of 16 O2. The two unpaired electrons of the oxygen molecule lead to an electron spin angular momentum S = 1. The sum of spin angular momentum, S, and the rotational angular momentum, K, gives three possible total angular momentum states J =0, 1, 2for the K = 1 ground state (J = K + S, electron orbital angular momentum in the Σ state is zero). In the weak-field Zeeman regime, the three total angular momentum states each split into 3 sub-levels with different total angular momentum projections in the direction of the magnetic field. At high fields (above 2.5 T) the electron spin decouples from the rotational angular momentum and forms three different sets of three levels, where each set is almost-degenerate. The J =2,MJ = 2 sub-level has the highest magnetic moment both in the low and high field regions, which leads to the magnetic moment being approximately the same in both the low and high field regime. The magnetic moment of this sublevel is approximately equal to 1.8 Bohr magnetons [86]. This magnetic sublevel has an avoided level crossing with the J =2, MJ = 2 sub-level from the K = 3 manifold at about 8 T, changing its behavior from low-field to high-field seeking, which is incompatible with the coilgun as it is currently 110
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 and 92: the magnitude of the field some dis
Page 93 and 94: nozzle front surface aluminum catho
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: MCP Signal [arb. units] 2.0 1.5 (1)
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?