A method is reported for time- and space-resolved nonintrusive velocimetry of high-speed gas flows by measurement of the Doppler shift of light scattered from a laser-induced thermal grating. The principle is demonstrated by use of a pulsed frequency-doubled Nd:YAG laser to induce a thermal grating in NO<sub>2</sub> seeded into an argon flow. Signals are generated by Bragg scattering of probe beams at the fundamental frequency of the same Nd:YAG laser. Flow velocities in the range 30–180 ms<sup>-1</sup> are measured, in agreement with values obtained with a Pitot tube. The measurement uncertainties obtained indicate that a precision of 1% is feasible for flows at Mach 1.
© 1998 Optical Society of America
D. J. W. Walker, R. B. Williams, and P. Ewart, "Thermal grating velocimetry," Opt. Lett. 23, 1316-1318 (1998)