OPTICAL PROBE DETECTION OF HIGH-FREQUENCY SURFACE ACOUSTIC-WAVES GENERATED BY PHASE-VELOCITY SCANNING OF LASER INTERFERENCES FRINGES

Laser-generated high-frequency surface acoustic waves (SAWs) and their optical detection for noncontact and nondestructive materials evaluation were presented. Scanning interference fringes (SIF) produced by intersecting two coherent pulsed laser beams on a tested object with different frequencies were used as a thermoelastic source to generate a 110 MHz SAW. The SAW was detected by the optical knife edge method using another continuous wave (CW) laser as a probe beam. Estimation of the SAW amplitude was carried out and the amplitude enhancement eff ect of the phase velocity scanning (PVS) method-was verified. As a result, the S AW amplitude of 1.4 nm was obtained on an aluminum specimen with 0.71 MW/cm2 power density of second-harmonic waves (532 nm) of a Q-switched Nd:YAG laser. An application to anisotropic SAW velocity measurement on a silicon (100) surface was carried out.