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

We report single-pulsed, spatially-resolved temperature measurements in unseeded low-speed and supersonic air using the acoustic decay of laser-created thermal gratings. A low energy 193 nm excitation scheme was employed to create 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 laser. This technique is insensitive to laser energy fluctuations as it is a frequency rather than an intensity measurement. Single-pulse measurements in Mach 3.9 and Mach 2.0 nozzle flows were analyzed to a temperature uncertainty of better than 7% by use of power spectra of the time domain signals. Higher accuracy is expected with improved calibration measurements. (C) 1999 Elsevier Science B.V. All rights reserved.