In-situ characterization using pulsed laser systems and hyperspectral imaging

We are investigating the use of resonance-enhanced multiphoton ionization (REMPI) to detect volatile organic compounds (VOCs) mainly BTEX compounds (benzene, toluene, ethylbenzene, o-, m -, and p-xylenes) and some organochlorides, such as tetrachloroethylene (PCE), trichloroethylene (TCE), and carbon tetrachloride, found in the environment. The long term objective of this work is to develop a system for measuring and identifying a wide range of VOCs at part-per-billion levels in the environment in-situ in the subsurface. The specific focus of this work is to identify and optimize the experimental parameters that affect the determination of these organic compounds using the REMPI technique.; REMPI is a spectroscopic technique that is advantageous for in-situ analyses involving VOCs found as contaminants in the environment. REMPI can give quantitative and qualitative information about these compounds and it has the capability to detect specific contaminants and distinguish them from other species in the sample. The REMPI technique is well-suited to detect these compounds since selective ionization of the species of interest occurs.; This research involves the development of a fiber-optic REMPI probe. Our current prototypes include lensed and non-lensed probe designs. However, the main focus of this dissertation is the optimization of the non-lensed probe design. The primary volatile organic compounds that this dissertation will address are the BTEX compounds, benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes. These VOCs will be analyzed using REMPI in order to determine the best conditions and parameters appropriate for each species. This involves the determination of the optimal laser wavelength for each species, both alone and in mixtures. For these studies, partial least squares (PLS) multivariate calibration is used to examine the REMPI excitation scans of various mixtures of BTEX compounds.; Hyperspectral imaging and laser-induced fluorescence are also discussed in this dissertation. The study involving hyperspectral imaging demonstrates a novel way to make 2-dimensional temperature “maps” of flames using a dimension reduction fiber array by measuring iron emission from the flame. Laser ablation along with LIF are performed together to monitor the effect of flame retardant chemicals in the combustion environment by measuring OH radical fluorescence and fluorescent lifetime.