Temperature measurement in a supersonic flow with resonant laser-induced thermal gratings

1999 by Princeton University. 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 O2in 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 are analyzed to a temperature uncertainty of better than 7% by use of Fourier transform. Higher accuracy is expected using curve-fitting techniques. The technique was applied to temperature measurements in a series of experiments demonstrating controlled energy addition to a supersonic flow with a 50 kW electron beam. Selected results from these experiments are presented.

Temperature measurement in a supersonic flow with resonant laser-induced thermal gratings Conference Paper