Roger Ding Dr. Daniel S. Elliott John Lorenz July 29, 2010
Overall Project Goal: Photoassociation of Li and My REU Goals: Work on electronics to help control the dualspecies magneto-optical trap (MOT) Laser locking circuits Timing Controls
Trapping Laser Repump Laser Li Trapping and Repump Laser Locking Circuit 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 Li? 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 force 2. Position-dependent force
Principle ideas: Photons carry momentum Atoms can absorb photons Conservation of momentum Doppler shift
~780nm 85 2 2 P 3/2 120.65 MHz 4 3 63.40 MHz 2 29.37 MHz 1 p=hf/c Conservation of Momentum 2 2 P 1/2 361.58 MHz 3 2 D 1 794.979 nm D 2 780.241 nm 85 v 2 2 S 1/2 85 3035.73 MHz 3 2 J. Lorenz
Atom at rest: f L,L 85 f L,R Atom moving towards the right: f L,L - f D 85 f L,R + f D v
Red-detune the laser from the transition frequency by Slow moving atoms f L,L 85 f L,R f L L R Fast moving atoms f L,L - f D F net 85 v f L,R + f D f L =f D =f D L R
Principle Ideas: Slow moving atoms Zeeman effect Selection rules
Slow Moving Atoms Too slow to Doppler shift laser onto resonance Zeeman Effect Used to shift atomic energy levels onto resonance f D f D E=g L B m F B f L f L
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 V Dichroic Atomic Vapor Laser Lock (DAVLL) Large capture range: Robust Tendency to drift f
Idea: take the derivative of the Doppler-free saturated absorption signal
Cell Cell 87 F=2 85 F=3 85 F=2 87 F=1 Doppler broadening 87 F=2 85 F=3 85 F=2 Hole burning 87 F=1
Cell 87 F=2 85 F=3 85 F=2 87 F=1 Doppler-free saturated absorption Physical implementation of Doppler-free saturated absorption
87 F=2 Doppler-free saturated 85 absorption 85 F=3 F=2 87 F=1 Look at 85 F=3 ground state 2-3 C.O. 2-4 C.O. 3-4 C.O. F=2 F=3 F=4 Close-up of 85 hyperfine peaks
Hyperfine Peaks Crossover Resonances F=3 F=3 +f D F=2 F=2 -f D F=3 F=3
1. Apply a dither to the Doppler-free saturated absorption signal Abs. Abs. Dither f 2. Use a lock-in amplifier and low-pass filter to convert amplitude of dither on signal to voltage Abs. V f Lock-in + Low-pass f f
Idea: in a magnetic field, atoms absorb light differently depending on its polarization
Abs. B + - Cell Abs. f f
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 acoustooptic 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 Amplifier Acousto-Optic Modulator (AOM) National Instruments Card x6 Voltage Controlled Oscillator (VCO) Amplifier Acousto-Optic Modulator (AOM) 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