Diagnostics in gases by transient laser-induced electrostrictive gratings

We applied time resolved light diffraction from electrostrictive gratings to measure non-intrusively gas compositions and temperatures. The infrared radiation of a pulsed Nd:YAG laser generates a spatially periodic density grating that oscillates in time and the beam of a continuous-wave laser or a train of pulses provided by an external cavity is used to read it out. The oscillation period of the grating diffraction efficiency depends on the sound velocity in the medium. If the gas composition is known the measurement of the sound velocity allows to deduce the temperature. We evaluated this novel technique in an open tube furnace for temperatures in air up to about 1400 K. On the other hand, if the temperature is known, concentrations in isothermal binary mixtures can be determined by the laser-induced grating technique. Measurements were performed in methane/nitrogen and hydrogen/nitrogen mixtures.