Measurement of gas-phase sound speed and thermal diffusivity over a broad pressure range using laser-induced thermal acoustics

We report on the detection and analysis of signals generated from gas-phase laser-induced gratings over a large range of static pressure (0.04-100 atm). We employed the experimental technique of laser-induced thermal acoustics and performed measurements on mixtures of NO(2) in air and CO(2) as a function of pressure. Accurate analysis of the acquired data was obtained from a full theory, including beam size effects. The theory fully reproduces the observed data for a ratio of molecular mean free path to grating wavelength extending from 1 to 4 x 10(-4). Nonlinear, least-squares f its between modeled and experimental signals provided accurate values of the sound speed and thermal diffusivity.