Departmental Oral Examination (Thesis Title: "High Resolution Two-Photon Spectroscopy of 129Xe for Precision Optical Magnetometry")
Physics and Astronomy
This dissertation presents high precision two-photon xenon spectroscopy of the 5p5(2P3/2)6p 2[3/2]2 -> 5p6 (1S0) transition. Experimental results of the spectroscopic signal over pressures of 15 980 mTorr, combined with a theoretical discussion, led to the determination of the natural linewidth of the excited state. Specific attention is payed to the (F = 3/2) hyperfine level of 129Xe, motivated by the new experiment at TRIUMF to measure the electric dipole moment of the neutron (nEDM), where 129Xe will be used as an optical comagnetometer. A non-zero value of the nEDM would partially confirm the existence of the baryon asymmetry in the universe as predicted by the standard model. The experiment at TRIUMF aims increase the sensitivity of the current nEDM limit by increasing the number of ultra-cold neutrons and employing a cohabiting 199Hg/129Xe dual species comagnetometer.
The first experimental success was the technological development of the continuous wave 252 nm ultra-violet (UV) laser system, with the power and precision to selectively probe the hyperfine levels of 129Xe. Using this laser system the first high resolution spectrum of the two-photon transition was measured. Ten transition peaks are observed for the six most abundant isotopes in xenon gas, along with the hyperfine levels of the 129Xe and 131Xe isotopes. Analysis of this spectrum led to direct determinations of the hyperfine constants of the 5p5(2P3/2)6p2[3/2]2 excited state and constants relating to the isotope shift.
The final part of the dissertation focused on the parameterization of the 129Xe (F = 3/2) spectral line. In the nEDM experiment the pressure of 129Xe is limited to 3 mTorr, making it essential to characterize the signal at this level in order to maximize the sensitivity of the comagnetometer. This work presents a pressure dependence study of the spectral lineshape from 980-15 mTorr. These results illustrate the expected signal size and relative transition frequency to the (F = 3/2) level for precision laser tuning. In addition to the contributions of this work to optical magnetometry, the results present a complimentary experimental technique to determine the natural linewidth of the 5p5(2P3/2)6p2[3/2]2 excited state. The high precision of the results permit extrapolation of the lineshape to zero pressure yielding a natural linewidth of 4.3(1.6) MHz/Torr. Overall, the work presented is significantly important to optical magnetometry in nEDM experiments, as well as to precision spectroscopy and theories of atom-atom interactions.