OPTICAL PROBING OF SURFACE RAYLEIGH WAVES

Abstract

Data are presented on optical probing of Raleigh surface waves by Brillouin diffraction of light. The apparatus uses a low‐cost 3‐mW He–Ne laser and is shown to be a simple and convenient tool for acoustic losses and velocity measurements. The minimum acoustic amplitude detectable is 0.1 Å and the phase velocity is measured with an accuracy better than 0.6%. We give a simple explanation of the spatial distribution of the acoustic flux and show that in a 6‐μsec quartz delay line, losses due to beam spreading are two times greater than the intrinsic loss. The results obtained with gold‐coated surfaces indicate that the acoustic beam spreading is very pronounced and can partially alter some conclusions given in previous communications.