Generation and temporally resolved detection of laser-induced gratings by a single, pulsed Nd : YAG laser

The infrared radiation of a pulsed Nd:YAG laser is employed to generate, ei ther by electrostriction or by thermalization of absorbed laser energy, a s patially periodic density grating that oscillates in time. The second-harmo nic output of the same laser is injected into a high-reflectance optical ca vity, and the pulse trapped in the cavity is used to monitor the temporal e volution of the grating diffraction efficiency. The oscillation period of t he diffraction efficiency depends on the sound velocity in the medium. If t he gas composition is known, measurement of the sound velocity allows the t emperature to be deduced. On the other hand, if the temperature is known, c oncentrations in isothermal binary mixtures can be determined. We demonstra te the applicability of this novel one-laser grating arrangement by concent ration measurements in a cell containing methane-nitrogen mixtures and by p reliminary temperature measurements in a premixed methane-air flame. (C) 19 99 Optical Society of America.