Thermal grating and broadband degenerate four-wave mixing spectroscopy of OH in high-pressure flames

Abstract

∑–X2Π(0,0) band of OH has been studied in premixed methane/air flames using a cw Ar+ laser probe. Measurements of flame temperature and pressure were derived from fits of theoretical simulations to the observed time variation of signals over a pressure range of 10 to 40 bar and for different stoichiometry that were in agreement with independent measurements using N2 CARS and predictions of a one-dimensional flame calculation. Broadband DFWM spectra in the same band of OH were observed up to a pressure of 9 bar, above which signals were obtained only from scattering from thermal gratings.