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Title: Remote Detection of Trace Species for Combustion and Atmospheric Magnetometry
Authors: Chng, Tat Loon
Advisors: Miles, Richard B
Contributors: Mechanical and Aerospace Engineering Department
Keywords: Laser Diagnostics
Remote Detection
Subjects: Mechanical engineering
Aerospace engineering
Issue Date: 2017
Publisher: Princeton, NJ : Princeton University
Abstract: This thesis effort focuses on extending the development of radar REMPI, a laser-based diagnostic, for concentration measurements. Radar REMPI combines the selective ionization of resonance enhanced multi-photon ionization spectroscopy (REMPI) with the high detection sensitivity afforded by coherent microwave scattering (radar). The incorporation of microwaves not only permits sub-ns temporal resolution of the concentration measurement but also supports long distance propagation required for remote sensing applications. Here, the development of radar REMPI is facilitated by evaluating its performance with respect to two different applications, namely, the measurement of combustion species and the use of trace species for atmospheric magnetometry. While the underlying physics of both these fields are relatively distinct, they share a common need for trace species detection in environments with a multitude of buffer gases. A primary contribution of this thesis is the observation that the amount and type of buffer gas has a significant impact on both the amplitude and temporal dynamics of the radar REMPI signal. Measurements of radical species in a combustion environment have been conducted by probing atomic oxygen (O) in a well-calibrated flame produced by a Hencken burner. Absolute O concentrations are obtained via calibration against an inert gas (i.e. xenon (Xe)) with a similar REMPI scheme. Buffer gas effects are avoided by seeding known amounts of Xe into the flame and performing the calibration in-situ. The results generally agree well with their expected equilibrium concentrations, but display an overshoot in both the fuel-rich and fuel-lean regimes, a phenomenon which is likely to be due to laser photolysis. A framework for utilizing the 129Xe isotope as the magnetic medium for atmospheric magnetometry has been proposed and partially demonstrated. The concept involves spin polarizing and measuring the long-lived magnetic field precession of 129Xe, which has a native concentration of about 24 ppb in the atmosphere. Suitable two-photon Xe transitions have been identified and detection sensitivities of < 150 ppb in pure N2 and < 1.5 ppm in air have been successfully realized using radar REMPI. A spin polarization scheme using two-photon pumping on a deltaJ=0 transition around 249 nm has also been demonstrated.
Alternate format: The Mudd Manuscript Library retains one bound copy of each dissertation. Search for these copies in the library's main catalog:
Type of Material: Academic dissertations (Ph.D.)
Language: en
Appears in Collections:Mechanical and Aerospace Engineering

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