Anisotropic MOT for Nonlinear Optical Studies
Joel A. Greenberg, Marcos Oria*, Daniel J. Gauthier
Quantum Electronics Lab, Physics Department, Duke University
Optics:
Introduction
Trap Characteristics
3 cm
Vacuum
Trapping
Goals:
• Develop a simple MOT geometry to produce an
anisotropic, high density trap
• Use the MOT to study nonlinear optical effects
1cm
Mirror
y
Cell
x
z
Probe
Experimental Setup
Magnets
θ
Cooling
+
−
• Two reflected beams ( σ - σ ) for trapping (3cm x 2cm)
• Retroreflected off-axis beams for cooling (lin lin; d=1cm)
à Cooling beams also act as pump beams
• Probe along axis of MOT
Magnets:
• Length: ~3 cm Radius: 0.3 mm à Aspect Ratio 100:1
• Optical Depth ~12 (e-OD)
• Density 2x109 atoms/cm3
• Temperature ~20µK
3cm
Why Use Off-Axis Cooling Beams?
Citations
1) M. Vengalatorre, W. Rooijakkers, M. Prentiss. PRA 66, 053403 (2002)
2) J. Guo, P.R. Berman, B. Dubetsky, G. Grynberg. PRA 46, 1426 (1992)
3) A.M.C. Dawes, L. Illing, S. M. Clark, and D. J. Gauthier, Science 308, 672 (2005)
Funding
US Army Research Office (grant # W911NF-05-1-0228), DARPA (grant # Contract PO #412785-G-2)
400
300
200
100
z velocity
Cooling beams along z axis with different
forward:backward cooling beam power ratios
Recoil-Induced Resonance
- 2- 1 0 1 2 3
RIR Gain
z position
150
125
100
75
50
25
- 2- 1 0 1 2 3
z velocity
Rotation of Cooling Beams:
Gives less confinement along trap axis à Longer Trap
Gives more cooling in the z direction à Colder Trap
*Permanent Address: UNIVERSIDADE FEDERAL DA PARAÍBA
DEPARTAMENTO DE FÍSICA
LABORATÓRIO DE FISICA ATÔMICA E LASERS
RIR Model Fit
Model[2]
Data
0.8
7
6
5
4
3
2
1
0
-1
-500
0.6
Abs (arb)
z position
- 2- 1 0 1 2 3
• Can localize trap in z direction by
beam misalignment
• Atomic population can be
transferred quickly
θ = 0 rad
- 2- 1 0 1 2 3
700
600
500
400
300
200
100
Trap Localization/Transfer
1cm
Transmission
175
150
125
100
75
50
25
# of atoms (arb)
• Magnets external to vacuum
• Trap location 5 mm above magnets
• 4 oppositely poled µ metal cores (5x5x0.1 cm) [1]
• 200 turns for each magnet
• No need to cool magnets (Iouter/Iinner = 2, Iouter ~300 mA)
• Typical gradient: ∇ B= 10 G/cm ; Max ∇B= 30 G/cm
• Uses a simple vacuum system (p ~10-9 T)
• Rb supplied via getter (trap runs with getter off)
• Homemade cell constructed with AR coated windows
(3 cm cube)
• Cell base is gold mirror to produce beam geometry
• No magnetic compression currently used
θ = π /10 rad
# of atoms (arb)
1cm
# of atoms (arb)
MAGNETS
# of atoms (arb)
CELL
Results/Future Work
• 2D Model (x-z plane) to determine effect of beam geometry
• Atoms with vz injected into trap with cooling beams off z axis
• Considers:
- 2 level atom
- Classical trajectories
- Gaussian beam profile
- Absorption due to trap
- Perfect trapping in x-y plane
-300
-100
ν (kHz)
100
300
500
0.4
0.2
0
- 0.2
- 0.4
- 0.6
- 0.8
• RIR gain of 650%
• Trap run in steady state
ν (arb)
- 0.4
0
0.4
0.8
• Fit used for determining T
Future Work
• Look for instabilities and optical pattern formation[3]
• Look for collective spatial atomic behavior for enhanced
nonlinear response
• Look at RIR in strong probe regime for multiphoton effects