<title>Flame Diagnosis By Coherent Anti-Stokes Raman Spectroscopy</title>

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) is a promising diagnostic technique for the probing of flames and practical combustion environments. In this paper, the results of CARS investigations at UTRC in a variety of flames will be described. CARS thermometry has received the major emphasis in this work, but some species sensitivity studies will be reported as well. The CARS spectra are produced by mixing a 10 pps, frequency-doubled neodymium laser with a spectrally broadband, laser-pumped dye laser. In this approach, which avoids the need to frequency scan the dye laser, the entire CARS spectrum is generated in a single pulse, permitting instantaneous measurements of medium properties. A new crossed-beam phase-matching technique, termed BOXCARS, has been demonstrated for the first time and is described. This approach, which will be extremely useful in studies of stratified flames, leads to greatly enhanced and unambiguous spatial resolution, in contrast to the conventional collinear phase-matching approaches. Utilizing this technique, CARS temperature measurements are reported in a variety of structured flames including sooting, hydrocarbon-fueled diffusion flames. Moderate resolution CARS spectra from hot N2 obtained by scanning the spectrum in pre-mixed laminar flames show excellent agreement with computer generated spectra. The spectra display a number of very interesting features, such as the appearance of individual Q-branches and hot band structure arising from the overlap of the v = 0 →4 and 1 → 2 bands. Low resolution CARS spectra have been obtained in a single pulse using an optical multichannel analyzer which also display good agreement with predicted spectra and which demon-strate the feasibility of single pulse thermometry. CARS species sensitivity limitations have been explored in an investigation of CO detectability levels in flames.© (1978) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.