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Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang

Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang Department of Physics and Astronomy SUNY at Stony Brook May. 4 th , 2005. Doppler Effect in absorption spectroscopy. Maxwell velocity distribution. Sharp absorption line get broadened!.

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Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang

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  1. Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang Department of Physics and Astronomy SUNY at Stony Brook May. 4th, 2005

  2. Doppler Effect in absorption spectroscopy Maxwell velocity distribution Sharp absorption line get broadened! Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  3. Doppler-free absorption spectroscopy • Crossover transition peaks stronger than original transition peaks • pumping beam can create hyperfine pumping and saturation Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  4. External Cavity Diode Laser (ECDL) & Grating Feedback Laser Diode heat sink Littrow Configuration for grating feedback: PZT Grating 0th order: laser output 1st order: grating feedback Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  5. Optical Circuitry Layout Optic Isolator Rb cell Photo Diode Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  6. Tunable Parameters Temperature • change laser diode bandgap → coarse tuning • time-consuming • 4GHz / 0C Injection Current • shift and select the lasing mode • 40 MHz / mA Voltage bias applied on PZT • wave generator + amplifying circuit • offset → displacement • amplitude → range • DC voltage → limit Reduction rates Vosc:VPZT=1:100 Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  7. 87Rb energy levels Hamiltonian: Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  8. Rubidium spectrum 85Rb: 72%, I=5/2, Ground states F=2,3 87Rb: 28%, I=3/2, Ground states F=1,2 Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  9. Coarse position tuning Some periodic pattern due to laser output frequency hops Parameters: Temp=22.70C Amp=2.12V Offset=1.84V Curr.=78.5A,78.8A “flashing” maximal frequency sweeping Fix the temperature and triangle wave voltage, tuning the injection current continuously within a small range 87Rb F=2→F’ 85Rb F=3→F’ Doppler-broadened absorption spectrum Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  10. 87Rb F=2→F’ fine structure Parameters: Temp=22.70C Amp=1.09V Offset=1.77V Curr.=79.0A F’=3 F’=2 F’=1 Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  11. 85Rb F=3→F’ fine structure Parameters: Temp=22.70C Amp=1.31V Offset=2.24V Curr.=78.6A F’=4 F’=3 F’=2 Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  12. Quantitative Analysis For 85Rb F=3→F’ channel 2 Horizontal 8.5div, vertical 262V 262V/8.5div = 30.8V/div Horizontal scale zoom-in 2.5 times Two strongest peaks 30MHz/0.4div=75MHz/div Before zoom-in: 187.5MHz/div So, the response for output f to PZT V is 225MHz/30.8V=6.1MHz/V Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  13. Quantitative Analysis For 87Rb F=2→F’ channel 2 Horizontal 8.5div, vertical 218V 218V/8.5div = 25.7V/div Horizontal scale zoom-in 3 times 2nd and 3rd strongest peaks 128.6MHz/3.5div=36.7MHz/div Before zoom-in: 110MHz/div So, the response for output f to PZT V is 110MHz/25.7V=4.28MHz/V Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  14. Quantitative Analysis Finally, the response for output frequency to PZT Voltage is about 5.2+/-0.9 MHz/V Back to our coarse position tuning, 424V of scanning voltage amplitude corresponds to 2.205GHz of frequency sweeping range, thus can only reveal two neighboring Doppler-broadened absorption peaks. Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

  15. References • Daryl W. Preston, “Doppler-Free Saturated Absorption”, ELECTRO-OPTIC EXPERIMENTS FOR THE ADVANCED LABORATORY, 2000 • Bob Azmoun and Susan Metz, “RECIPE FOR LOCKING AN EXTENDED CAVITY DIODE LASER FROM THE GROUND UP”, http://laser.physics.sunysb.edu/~bazmoun/RbSpectroscopy/ • Jan Max and Walter Kruger, “A NOVEL TECHNIQUE FOR FREQUENCY STABILISING LASER DIODES”, http://hubble.physik.uni-konstanz.de/jkrueger/thesis/thesis.html/ • Rita Kalra, experiment log book in Laser Teaching Center Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

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