THERMAL GRATING AND BROAD-BAND DEGENERATE 4-WAVE-MIXING SPECTROSCOPY OF OH IN HIGH-PRESSURE FLAMES

Time-resolved light scattering from thermal gratings induced by absorp tion of pulsed laser light resonant with transitions in the A(2) Sigma -x(2)Pi(0, 0) band of OH has been studied in premixed methane/air flam es using a cw Ar+ laser probe, Measurements of flame temperature and p ressure were derived from fits of theoretical simulations to the obser ved time variation of signals over a pressure range of 10 to 40 bar an d for different stoichiometry that were in agreement with independent measurements using N-2 CARS and predictions of a one-dimensional flame calculation. Broadband DFWM spectra in the same band of OH were obser ved up to a pressure of 9 bar, above which signals were obtained only from scattering from thermal gratings.