Laser-induced thermal acoustics (LITA) was used with heterodyne detection to measure simultaneously and in a single laser pulse the sound speed and flow velocity of NO><sub>2</sub> -seeded air in a low-speed wind tunnel up to Mach number <i>M</i> =0.1 . The uncertainties of the velocity and the sound speed measurements were ∼0.2 m/s and 0.5%, respectively. Measurements were obtained through a nonlinear least-squares fit to a general, analytic closed-form solution for heterodyne-detected LITA signals from thermal gratings. Agreement between theory and experiment is exceptionally good.
© 2000 Optical Society of America
(000.2170) General : Equipment and techniques
(050.2770) Diffraction and gratings : Gratings
(120.6780) Instrumentation, measurement, and metrology : Temperature
(120.7280) Instrumentation, measurement, and metrology : Vibration analysis
(190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
Stefan Schlamp, Eric B. Cummings, and Thomas H. Sobota, "Laser-induced thermal-acoustic velocimetry with heterodyne detection," Opt. Lett. 25, 224-226 (2000)