Development of Laser-Induced Grating Spectroscopy for Application in Shock Tunnels

Abstract

An optical setup for laser-induced grating spectroscopy is presented. This setup provides the possibility to induce and analyze electrostrictive gratings as well as thermal gratings. Switching between the techniques can be realized smoothly. Temperature measurements were carried out at different test gas conditions in a temperature range from 20 to 70°C and a pressure range from 0.1 to 2 MPa using a test chamber made of stainless steel. The optically measured temperature was compared with simultaneously recorded thermocouple data to demonstrate the feasibility of the presented method. As a sufficient amount of an absorbing species in the test gas is required for the formation of a thermal grating, the experiments were performed on nitrogen monoxide with concentrations of 10 and 125 ppm, respectively, diluted in molecular nitrogen. Thereby, the higher concentration favors the formation of a thermal grating. Because of the planned application of the setup on a shock tube and a shock tunnel, data gained from single-shot measurements were also compared with thermocouple data.