Roger Ding. Dr. Daniel S. Elliott John Lorenz July 29, 2010

Transcription

1 Roger Ding Dr. Daniel S. Elliott John Lorenz July 29, 2010

2 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

3 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)

4 Using light to form molecules from atoms J. M. Sage et al. Optical Production of Ultracold Polar Molecules

5 Why Li? Polar molecule More complicated than atoms Potential applications: Quantum computing D. DeMille. Quantum Computation with Trapped Polar Molecules

6 Magneto-Optical Trap Used to trap and cool atoms Requirements to trap atoms: 1. Velocity-dependent force 2. Position-dependent force

7 Principle ideas: Photons carry momentum Atoms can absorb photons Conservation of momentum Doppler shift

8 ~780nm P 3/ MHz MHz MHz 1 p=hf/c Conservation of Momentum 2 2 P 1/ MHz 3 2 D nm D nm 85 v 2 2 S 1/ MHz 3 2 J. Lorenz

9 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

10 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

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12 Principle Ideas: Slow moving atoms Zeeman effect Selection rules

13 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

14 Selection Rules In a magnetic field, atoms preferentially absorb light depending on its polarization University of Colorado. Advanced Optics Lab: Laser Cooling and Trapping

15 A. Mills. Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State Spectroscopy

16 I I - +

17 Lasers must be tuned and kept at specific frequencies Stabilizing lasers: Temperature control Current control Electronic feedback

18 Peak Locking Small capture range: Accurate Sensitive to disturbances V Dichroic Atomic Vapor Laser Lock (DAVLL) Large capture range: Robust Tendency to drift f

19 Idea: take the derivative of the Doppler-free saturated absorption signal

20 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

21 Cell 87 F=2 85 F=3 85 F=2 87 F=1 Doppler-free saturated absorption Physical implementation of Doppler-free saturated absorption

22 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

23 Hyperfine Peaks Crossover Resonances F=3 F=3 +f D F=2 F=2 -f D F=3 F=3

24 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

25 Idea: in a magnetic field, atoms absorb light differently depending on its polarization

26 Abs. B + - Cell Abs. f f

27 A. Mills. Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State Spectroscopy

28 Want benefits of both peak locking and DAVLL schemes Accurate Robust Brute force approach Peak Locking DAVLL + _ Error Signal

29 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

30 Need method of controlling multiple acoustooptic modulators for the dual-species MOT Interface with National Instruments data acquisition card

31 AOMs are used for: Frequency shifting Fast shutters RP Photonics Acousto-optic Modulators

32 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

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35 My projects involved working on control mechanisms for the dual-species MOT Laser locking circuits AOM controller board

36 Dr. Daniel S. Elliott Dr. Sergei Savikhin John Lorenz Adeel Altaf Dionysios Antypas