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

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

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

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

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

6. 6 Temperature change laser diode bandgap → coarse tuning time-consuming 4GHz / 0 C 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 Tunable Parameters Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 Reduction rates V osc :V PZT =1:100

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

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

9. 9 Coarse position tuning Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 “flashing” maximal frequency sweeping 87 Rb F=2→F’ 85 Rb F=3→F’ Doppler-broadened absorption spectrum Some periodic pattern due to laser output frequency hops Fix the temperature and triangle wave voltage, tuning the injection current continuously within a small range Parameters: Temp=22.7 0 C Amp=2.12V Offset=1.84V Curr.=78.5A,78.8A

10. 10 87 Rb F=2→F’ fine structure Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 F’=3 F’=2 F’=1 Parameters: Temp=22.7 0 C Amp=1.09V Offset=1.77V Curr.=79.0A

11. 11 85 Rb F=3→F’ fine structure Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 F’=4 F’=3 F’=2 Parameters: Temp=22.7 0 C Amp=1.31V Offset=2.24V Curr.=78.6A

12. 12 Quantitative Analysis Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 For 85 Rb 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

13. 13 Quantitative Analysis Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 For 87 Rb F=2→F’ channel 2 Horizontal 8.5div, vertical 218V 218V/8.5div = 25.7V/div Horizontal scale zoom-in 3 times 2 nd and 3 rd 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

14. 14 Quantitative Analysis Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 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.

15. 15 Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4 th,2005 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/ 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/ http://hubble.physik.uni-konstanz.de/jkrueger/thesis/thesis.html/ Rita Kalra, experiment log book in Laser Teaching Center