Optical detection of ultrasound at a distance using a confocal Fabry–Perot interferometer

Abstract

A novel scheme to detect ultrasonic motion at the surface of a solid sample is presented. The surface of the sample is illuminated by a laser and the light scattered by the surface is received by a confocal Fabry–Perot interferometer which demodulates the Doppler shift produced by ultrasound. Experimental results, obtained at a distance of 1.5 m from a machined but not polished steel plate, and excited by ultrasound produced by a laser pulse, are presented.