Investigations of coherent anti-Stokes Raman spectroscopy /CARS/ for combustion diagnostics

Abstract

Investigations of coherent anti-Stokes Raman spectroscopy (CARS) in a variety of flames are presented. Thermometry has received the primary emphasis in these studies, but species spectral and sensitivity studies will also be described. CARS is generated by mixing a 10 pps, frequency-doubled neodymium 'pump' laser with a spectrally broadband, laser-pumped, Stokes-shifted dye laser. This approach obviates the requirement to frequency scan the dye laser and generates the entire CARS spectrum with each pulse permitting, in principle, instantaneous measurements of medium properties. CARS spectra of N2, CO, O2, H2O, CO2 and CH4 in flames will be presented. In general these spectra exhibit very good agreement with computer synthesized spectra and permit measurements of temperature and species concentration. To illustrate the applicability of CARS to practical combustion diagnostics, CARS signatures from N2 have been employed to map the temperature field throughout a small, luminous, highly sooting propane diffusion flame