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Resonant Faraday Rotation in a Hot Lithium Vapor

Resonant Faraday Rotation in a Hot Lithium Vapor . Scott Waitukaitis University of Arizona, Department of Physics May 2007. Overview. Highly frequency dependent Can be enhanced near resonances . How does this work?. Linearly polarized light is a superposition of equal parts RCP and LCP

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Resonant Faraday Rotation in a Hot Lithium Vapor

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  1. Resonant Faraday Rotation in a Hot Lithium Vapor Scott Waitukaitis University of Arizona, Department of Physics May 2007

  2. Overview • Highly frequency dependent • Can be enhanced near resonances

  3. How does this work? • Linearly polarized light is a superposition of equal parts RCP and LCP • RCP and LCP have different indices • Resulting rotation proportional to difference in indices, i.e.

  4. The role of B: the Zeeman effect • RCP light causes • LCP light causes • Via Zeeman effect, degeneracy in is lifted so that

  5. Frequency dependence

  6. Fine structure of lithium • Wavelength range ~0.04 nm • Frequency range ~30 GHz -3/2 -1/2 1/2 3/2 -3/2 -1/2 1/2 3/2 -1/2 1/2 -1/2 1/2 670.9510 nm 670.9785 nm 670.9761 nm 670.9919 nm -1/2 1/2 -1/2 1/2

  7. Added complexities • Natural linewidth ~6 MHz • Observed width ~3000 MHz • Broadening mechanisms • Doppler broadening • Power broadening • Pressure broadening

  8. What do we need to observe Faraday rotation? • A laser that can be tuned over a 0.04 nm range around 670 nm • A lithium vapor • A way to infer rotation has occured

  9. Diode laser basics • l ~ 670 nm • Wavelength is modulated via current adjustment • As wavelength changes so does output power ~0.5 cm

  10. Laser output • Mode profile governed by boundary conditions of lasing medium • At a given temperature, lasing occurs where product of profiles is highest • Both mode and gain profile change with temperature • Dominant wavelength bounces from one mode to the next

  11. Typical laser trace

  12. Piezo driven external cavity • Piezos driven by function generator and control circuit • Able to adjust plate offset • Able to adjust amplitude of plate oscillations

  13. Heat pipe oven • ~ 3 cm in diameter • ~ 30 cm in length • ~ 650-700 K

  14. Experimental setup

  15. Data vs. model • Most general features of data mimicked by model • Sign • Order of magnitude • Model predicts more active features

  16. Possible causes of discrepancy • Hyperfine splitting in the ground state (~800 MHz) • Saturation effects due to high intensity of laser beam • Off-axis B field • Large laser line width

  17. Acknowledgments I’d like to thank Dr. Cronin for giving me the opportunity to work with him. I’d also like to thank Dr. Bickel for his advice along the way. My gratitude also goes out to Tori Carr, Yancey Sechrest, Vincent Lonij, Ben McMorran, John Perrault for their help and support as well.

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