Date on Master's Thesis/Doctoral Dissertation

5-2024

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Liu, Jinjun

Committee Co-Chair (if applicable)

Herring, Nicole

Committee Member

Herring, Nicole

Committee Member

Davis, Erin

Committee Member

Samuelsen, Chad

Committee Member

Farmer, Russell

Committee Member

Shaw, Monica

Author's Keywords

Spectroscopy; mid-infrared; laser; optics; molecules; doppler-free; cavity-ring-down

Abstract

This research documents steps towards building a novel spectroscopic technique, namely, cavity-enhanced double-resonance (CEDR) spectroscopy, for investigating methane (CH4) and other molecules with significance in astrochemistry. These efforts focus on tackling the complexities of their ro-vibrational energy levels and the inefficiencies in analyzing vibrational spectra, particularly for molecules with high symmetry and strong intramolecular interactions. In the CEDR spectroscopy, the first photon, generated by a continuous-wave optical parametric oscillator (CW-OPO) locked to a Doppler-free saturation absorption line, excites the molecule from its ground level to a selected excited ro-vibrational (rotational-vibrational) level, e.g., that of the asymmetric CH-stretch mode. The second photon then detects transitions from this intermediate level to a higher one with high-sensitivity spectroscopic techniques like cavity ring-down (CRD). The saturation absorption spectrum of the Q branch of CH4's ν3 = 1 band has been recorded with an average linewidth (FWHM) of 4.5 MHz and a frequency accuracy of ~3 MHz, achieved using previous optical-frequency-comb-based frequency measurement of selected lines and a home-built etalon. The new CW-OPO-based Doppler-free saturation spectroscopy system enables unprecedented scan capabilities, spectral resolution, and frequency accuracy in the mid-infrared. for 12 transitions. Proof-of-principles CW-CRD spectra of atmospheric water (H2O) have also been recorded. The ongoing research project aims at supporting the James Webb Space Telescope (JWST) observations in the infrared region and guide observations of ground-based radio telescope such as Green Bank and ALMA in the microwave and millimeter-wave regions.

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