Publications

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Time-resolved picosecond pure-rotational coherent anti-Stokes Raman spectroscopy is demonstrated for thermometry and species concentration determination in flames. Time-delaying the probe pulse enables successful suppression of unwanted signals. A theoretical model is under development. ©2010 Optical Society of America.

We review three photofragmentation detection approaches, describing the detection of (1) vapor-phase mercuric chloride by photofragment emission, (2) vapor-phase nitro-containing compounds by photofragmentation-ionization, and (3) surface-bound organophosphonate compounds by photofragmentation-laser-induced fluorescence. © 2010 Optical Society of America.

Effects of gas-phase collisions on active optical sensing and use of picosecond laser spectroscopy for their characterization are reviewed. Additionally, novel time-resolved approaches to reduce collisional sensitivity and to exploit species-dependent collision rates are discussed. ©2009 Optical Society of America.

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The author will describe two-photon-resonant LIF detection of CO, O, and H. Application of these techniques in flames frequently suffers from significant photolytic interferences caused by the intense UV excitation pulses required to produce measurable signal. When compared to nanosecond excitation, the use of short pulse (picosecond) excitation can significantly reduce the effect of the photolytic interference. Results of recent atomic oxygen imaging experiments using picosecond- and nanosecond-duration laser pulses will be presented, and potential improvements to CO and H imaging will be discussed.

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Two-color resonant four-wave-mixing spectroscopy (TC-RFWM) is used to investigate ground-state energy transfer of hydroxyl radical in atmospheric-pressure flames. Two amplified distributed-feedback dye lasers produce 50-ps, nearly transform-limited, infrared (IR) and ultraviolet pulses. The infrared pump laser is tuned to individual rovibrational transitions of OH X {sup 2}{pi}{sub 3/2} (v{prime}=1, N{prime}) {l_arrow} X {sup 2}{pi}{sub 3/2} (v{double_prime}=0, N{double_prime}), and the ultraviolet pulse probes either the directly pumped or collisionally populated intermediate levels via A{sup 2}{Sigma}{sup +} (v*=1, N*) {l_arrow} X{sup 2}{pi}{sub 3/2}(v{prime}=1, N{prime}). By time-delaying the probe pulse with respect to the pump pulse, and appropriately constraining the polarizations of each of the four fields taking part in the wave-mixing process, we are able to independently and unambiguously measure the moments of the rotational angular momentum distribution in single rotational levels of the ground state. We present measurements of population, alignment, and orientation decay in X {sup 2}{pi}{sub 3/2} for several flame conditions. These experiments provide data necessary for the development of accurate models for diagnostic techniques using saturating laser pulses.

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