DETECTION OF ULTRASONIC MOTION OF A SCATTERING SURFACE BY 2-WAVE MIXING IN A PHOTOREFRACTIVE GAAS CRYSTAL

The performance of an interferometric system based on two-wave mixing at 1.06 mum in undoped GaAs crystal, for the remote detection of trans ient motion of a scattering surface, is described. In this system, the wave scattered by the surface is mixed inside the photorefractive cry stal with a pump wave directly derived from the laser to provide the r eference wave of the interferometer. The system shows several features appropriate to industrial applications, although its sensitivity is l ess than passive interferometric systems of the confocal Fabry-Perot t ype presently in use, except in the low frequency range (below 1 MHz).