MEASUREMENT OF ACOUSTIC SURFACE WAVE PROPAGATION CHARACTERISTICS BY REFLECTED LIGHT

Abstract

This Letter reports on a novel method of recording acoustic surface wave patterns by reflected light. In this method the surface perturbations due to the sound wave act as a moving reflection grating, causing the reflected light to exhibit a phase corrugation which is a replica of the sound wave and moves in synchronism with it. At a certain distance from the grating this phase corrugation changes into a corresponding amplitude corrugation. A fixed grating located at this point, followed by a photomultiplier, serves to extract an electrical signal at the original sound frequency. This signal of which the amplitude is proportional to the surface perturbation is fed to an X‐Y recorder. By slowly moving the substrate on which the surface wave travels, a recording is made of the surface wave pattern in any desired cross section. Examples are given of 8 MHz standing and traveling surface wave patterns on a ferroelectric ceramic substrate.