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

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

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

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= C Amp=2.12V Offset=1.84V Curr.=78.5A,78.8A

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= C Amp=1.09V Offset=1.77V Curr.=79.0A

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= C Amp=1.31V Offset=2.24V Curr.=78.6A

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 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 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 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”, Jan Max and Walter Kruger, “A NOVEL TECHNIQUE FOR FREQUENCY STABILISING LASER DIODES”, Rita Kalra, experiment log book in Laser Teaching Center