DIRECT EXPERIMENTAL INVESTIGATIONS OF ACOUSTIC MODES GUIDED BY A SOLID-SOLID INTERFACE USING OPTICAL INTERFEROMETRY

This paper presents direct field measurements of acoustic modes guided by the interface between two transparent solids. The measurement tech nique is based on the acousto-optical interaction inside the solid bet ween the acoustic field and the probe laser beam of an interferometer. The main advantage of the method is its ability to measure acoustic s train fields in areas of difficult access with the classic detection m ethods. Moreover, it gives complete information about the dilatation s train field inside the solid, e.g., amplitude and phase. The propagati on of a real velocity mode (Stoneley wave) is first illustrated, Then the situation of complex velocity modes is investigated for a Plexigla s-fused quartz slip interface. This material combination supports two possible interface modes theoretically. These modes are simultaneously observed and the differences between their behavior are measured. (C) 1997 Acoustical Society of America.