Laser-induced thermal acoustics (LITA), an optical four-wave mixing technique, has been used for sensitive measurement of the sound speed, thermal diffusivity, acoustic damping rate, and complex susceptibility of a gas. In LITA, laser-induced acoustic waves scatter laser light into a coherent, modulated signal beam. A simple expression accurately describes the signal. Atmospheric sound speeds accurate to 0.5% and transport properties accurate to 30% have been measured in a single shot without calibration. LITA spectra have been taken of weak spectral lines of NO2 in concentrations of less than 50 parts in 109. Signal reflectivities up to 10−4 are estimated.
© 1994 Optical Society of America
Original Manuscript: February 17, 1994
Published: September 1, 1994
E. B. Cummings, "Laser-induced thermal acoustics: simple accurate gas measurements," Opt. Lett. 19, 1361-1363 (1994)