Single-pulse temperature measurement in supersonic air flow with predissociated laser-induced thermal gratings

We report single-pulsed, spatially-resolved temperature measurements in uns eeded low-speed and supersonic air using the acoustic decay of laser-create d thermal gratings. A low energy 193 nm excitation scheme was employed to c reate thermal gratings by predissociation of O-2 in the flow. The acoustic decay was monitored over a few hundred ns by a continuous-wave argon-ion la ser. This technique is insensitive to laser energy fluctuations as it is a frequency rather than an intensity measurement. Single-pulse measurements i n Mach 3.9 and Mach 2.0 nozzle flows were analyzed to a temperature uncerta inty of better than 7% by use of power spectra of the time domain signals. Higher accuracy is expected with improved calibration measurements. (C) 199 9 Elsevier Science B.V. All rights reserved.