There is demonstrated need for the capability to detect spectral signatures of trace gases at atmospheric pressure. While many remote sensing techniques are effective, they suffer limitations in their ability to discriminate trace gases at high pressures. This stems from the broadening of spectral lines washing away the spectral fingerprint as pressure increases. A double-resonance (DR) infrared (IR)/Terahertz (THz) ro-vibrational spectroscopy solution is proposed. The ability to discriminate between molecules or specific isotopic isomers of the same molecule using this double-resonance spectroscopy (DRS) technique comes from the unique pump source coincidence with the spectral lines of the trace gas and the probing of the transient changes in absorption seen in neighboring rotational transitions. These pump/probe combinations are unique to each isotopic isomer. In order to predict the behavior of this technique at atmospheric pressures, it must first be understood in the low-pressure regime. A set of experiments were conducted using a pulsed carbon dioxide (CO2) long-wave infrared (LWIR) laser pump source and THz probe source. The trace gas interrogated was methyl chloride 35 (CH335Cl) and the diluting gas was nitrogen (N2). Hyperfine frequency contributions were measured, and transient coherent behavior was observed. A model was also developed to simulate the coherent behavior at low-pressures and predict what is expected in the atmospheric regime. Experimental methods and results are discussed along with model output and predictions and a path toward atmospheric DRS experiments is detailed.
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Master of Science (M.S.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Masters Thesis (Campus-only Access)
Schneiderman, Max, "Measurement of Transient Coherent Effects in IR/THz Double Resonance Spectroscopy in the Low-Pressure Regime" (2022). Electronic Theses and Dissertations, 2020-. 1437.
Restricted to the UCF community until December 2027; it will then be open access.