LASER GENERATION AND DETECTION OF STRONGLY NONLINEAR ELASTIC SURFACE PULSES

Very high amplitude nonlinear surface acoustic wave pulses with 20-100 ns duration and acoustic Mach numbers up to 0.003 were excited in fus ed silica by nanosecond laser pulses acting on a strongly absorbing ov erlayer. Absolute measurements were performed with a calibrated dual-p robe-laser deflection setup. The formation of shock fronts during prop agation and nonlinear broadening of the wave form were observed for th e first time. Three nonlinear acoustic constants were evaluated and co mpared with values resulting from previously measured third-order elas tic moduli.