Observation of the lateral displacement of surface acoustic beams reflected at boundaries of layered substrates

The reflection of an acoustic surface wave incident on a velocity discontinuity is studied near the critical angle by using an optical-diffraction probe. The abrupt velocity change is implemented on fused quartz and on single crystal quartz substrates by plating the surface with a prism-shaped gold layer. A lateral displacement of the reflected beam, relative to the mirror-reflection path, is observed. For angles of incidence corresponding to total reflection, the phenomenon exhibits a behaviour which is similar to the Goos-Hänchen effect encountered at the total reflection of bounded electromagnetic waves. However, contrary to the electromagnetic case, it is found here that a significant lateral shift occurs also for angles well into the partial-reflection region and that the reflected beam profile is considerably distorted at the critical angle. These observations may be evidence of a leaky-wave mode along the boundary of the plated area, with the phase-matching condition satisfied at or near the critical angle.