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

Abstract

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 NO2 in air and CO2 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 fits between modeled and experimental signals provided accurate values of the sound speed and thermal diffusivity.