Laser-induced thermal acoustics: simple accurate gas measurements
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 10^9. Signal reflectivities up to 10^4 are estimated.
© Copyright 1994 Optical Society of America Received February 17, 1994 The author gratefully acknowledges the support of the University Research Initiative in aerothermochemistry sponsored by the U.S. Air Force Office of Scientific Research. The author is also indebted to the U.S. Office of Naval Research for its support of his graduate education through its fellowship program.