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 t hermal acoustics and performed measurements on mixtures of NO2 in air and CO2 as a function of pressure. Accurate analysis of the acquired d ata was obtained from a full theory, including beam size effects. The theory fully reproduces the observed data for a ratio of molecular mea n free path to grating wavelength extending from 1 to 4 x 10(-4). Nonl inear, least-squares fits between modeled and experimental signals pro vided accurate values of the sound speed and thermal diffusivity.