1 Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang Department of...

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Optic Rotation Project I

Doppler-free saturated absorption spectrum

Lei Huang

Department of Physics and Astronomy

SUNY at Stony Brook

May. 4th, 2005

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Doppler Effect in absorption spectroscopy

Lei Huang, Optic Rotation Project 1, Rb spectroscopy, May 4th,2005

Maxwell velocity distribution

ZZ

ZZ dVkT

MV

kT

MdVVP )

2exp()

2()(

22/1

Sharp absorption line get broadened!

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Doppler-free absorption spectroscopy


• Crossover transition peaks stronger than original transition peaks• pumping beam can create hyperfine pumping and saturation

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External Cavity Diode Laser (ECDL) & Grating Feedback


Laser Diode

GratingPZT

heat sink

Littrow Configuration for grating feedback:

Ldi

di

d

dm

2sin2, :order1st

)sin(sin

0th order: laser output1st order: grating feedback

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Optical Circuitry Layout


Rb cell

Optic Isolator

Photo Diode

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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

Tunable Parameters


Reduction ratesVosc:VPZT=1:100

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87Rb energy levels


...)(42 0

22

IJSLrr

eZ

m

pH eff

Hamiltonian:

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Rubidium spectrum


85Rb:72%, I=5/2,Ground states F=2,3

87Rb:28%, I=3/2,Ground states F=1,2

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Coarse position tuning


“flashing” maximal frequency sweeping

87Rb F=2→F’ 85Rb F=3→F’ Doppler-broadened absorption spectrum

Some periodic patterndue to laser output frequency hops

Fix the temperature and triangle wave voltage, tuning the injection current continuously within a small range

Parameters:Temp=22.70CAmp=2.12VOffset=1.84VCurr.=78.5A,78.8A

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87Rb F=2→F’ fine structure


F’=3 F’=2 F’=1

Parameters:Temp=22.70CAmp=1.09VOffset=1.77VCurr.=79.0A

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85Rb F=3→F’ fine structure


F’=4 F’=3 F’=2

Parameters:Temp=22.70CAmp=1.31VOffset=2.24VCurr.=78.6A

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Quantitative Analysis


For 85Rb F=3→F’channel 2Horizontal 8.5div, vertical 262V262V/8.5div = 30.8V/div

Horizontal scale zoom-in 2.5 times

Two strongest peaks 30MHz/0.4div=75MHz/divBefore zoom-in: 187.5MHz/divSo, the response for output f to PZT V is225MHz/30.8V=6.1MHz/V

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For 87Rb F=2→F’channel 2Horizontal 8.5div, vertical 218V218V/8.5div = 25.7V/div

Horizontal scale zoom-in 3 times

2nd and 3rd strongest peaks 128.6MHz/3.5div=36.7MHz/divBefore zoom-in: 110MHz/divSo, the response for output f to PZT V is110MHz/25.7V=4.28MHz/V

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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.

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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

http://laser.physics.sunysb.edu/~bazmoun/RbSpectroscopy/

http://hubble.physik.uni-konstanz.de/jkrueger/thesis/thesis.html/

1 Optic Rotation Project I Doppler-free saturated absorption spectrum Lei Huang Department of...

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