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Roger DingDr. Daniel S. Elliott
John LorenzJuly 29, 2010
Overall Project Goal:• Photoassociation of Li and Rb
My REU Goals:◦ Work on electronics to help control the dual-
species magneto-optical trap (MOT) Laser locking circuits Timing Controls
Rb Repump Laser
Locking Circuit
Li Trapping and Repump Laser
Rb Trapping Laser
Locking Circuit
Locking Circuit
Timing Control
Timing Control
Timing Control
Dual-Species Magneto-Optical Trap (MOT)
Using light to form molecules from atoms
J. M. Sage et al. “Optical Production of Ultracold Polar Molecules”
Why LiRb?◦ Polar molecule ◦ More complicated than atoms
Potential applications:◦ Quantum computing
D. DeMille. “Quantum Computation with Trapped Polar Molecules”
Magneto-Optical Trap◦ Used to trap and cool
atoms Requirements to trap
atoms:1. Velocity-dependent
force2. Position-dependent
force
Principle ideas:◦ Photons carry momentum◦ Atoms can absorb photons◦ Conservation of momentum◦ Doppler shift
85Rb~780nm
85Rb
J. Lorenz
3035.73 MHz
361.58 MHz
63.40 MHz
120.65 MHz
D2780.241 nm
85Rb2
3
3
2
2
3
4
22S1/2
22P1/2
22P3/2
29.37 MHz1
D1794.979 nm
Conservation of Momentum
v
p=hf/c
Atom at rest:
Atom moving towards the right:
85Rb fL,RfL,L
v85Rb fL,R + fDfL,L - fD
Red-detune the laser from the transition frequency by
Slow moving atoms
Fast moving atoms
85Rb fL,RfL,L
fL,L - fD fL,R + fD85RbvFnet
L R
fL
=fD=fD
L R
fL
Principle Ideas:◦ Slow moving atoms◦ Zeeman effect◦ Selection rules
Zeeman Effect Used to shift atomic
energy levels onto resonance
Slow Moving Atoms Too slow to
Doppler shift laser onto resonance
fD
fL
fL
fD
E=gL�BmFB
Selection Rules In a magnetic field, atoms preferentially
absorb light depending on its polarization
University of Colorado. “Advanced Optics Lab: Laser Cooling and Trapping”
A. Mills. “Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State
Spectroscopy”
+-
I
I
Lasers must be tuned and kept at specific frequencies
Stabilizing lasers:◦ Temperature control◦ Current control◦ Electronic feedback
Peak Locking
Small capture range:◦ Accurate ◦ Sensitive to
disturbances
Dichroic Atomic Vapor Laser Lock (DAVLL)
Large capture range:◦ Robust◦ Tendency to drift
f
V
Idea: take the “derivative” of the Doppler-free saturated absorption signal
Rb Cell Rb Cell
Doppler broadening “Hole burning”
87RbF=2
85RbF=3
85RbF=2
87RbF=1
87RbF=2
85RbF=3
85RbF=2
87RbF=1
Rb Cell
Doppler-free saturated absorption
87RbF=2
85RbF=3
85RbF=2
87RbF=1
Physical implementation of Doppler-free saturated absorption
F=3
2-3 C.O.
2-4 C.O.
F=4
3-4 C.O.
Close-up of 85Rb hyperfine peaks
F=2
Doppler-free saturated absorption87Rb
F=285RbF=3
85RbF=2
87RbF=1
Look at 85Rb F=3 ground state
Hyperfine Peaks Crossover Resonances
F=3
F=2
F=3
F=3
F=2
F=3
-fD
+fD
1. Apply a dither to the Doppler-free saturated absorption signal
2. Use a lock-in amplifier and low-pass filter to convert amplitude of dither on signal to voltage
Dither
Lock-in +Low-pass
f
Abs.
f
Abs.
f
Abs.
f
V
Idea: in a magnetic field, atoms absorb light differently depending on its polarization
f
Abs.
f
Abs.
Rb Cell+
-
B
A. Mills. “Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State
Spectroscopy”
Want benefits of both peak locking and DAVLL schemes◦ Accurate◦ Robust
Brute force approach
Peak Locking
DAVLL +
_ Error Signal
Have not yet had the chance to do extensive testing
Appears to be somewhat quirky:◦ Does not yet lock as well as we had hoped
Improvements:◦ Tweak component values◦ Adjust error signals◦ Better method of combining signals
Need method of controlling multiple acousto-optic modulators for the dual-species MOT
Interface with National Instruments data acquisition card
AOMs are used for:◦ Frequency shifting◦ Fast shutters
RP Photonics “Acousto-optic Modulators”
Voltage Controlled Oscillator
(VCO)
RF Switch
Voltage Controlled Attenuator
National Instruments Card
AmplifierAcousto-Optic
Modulator (AOM)
Voltage Controlled Oscillator
(VCO)
AmplifierAcousto-Optic
Modulator (AOM)
x6
x2
My projects involved working on control mechanisms for the dual-species MOT◦ Laser locking circuits◦ AOM controller board
Dr. Daniel S. Elliott Dr. Sergei Savikhin John Lorenz Adeel Altaf Dionysios Antypas
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