Giant surface acoustic waves generated by a multiple beam laser: Application to the detection of surface breaking slots

Giant surface acoustic wave (SAW) pulses have been generated by implementing on the surface of a solid an array of strip thermoelastic sources. It is shown experimentally, with a 16-beam pulsed YAG laser, that the delays introduced between the laser emission times allow the constructive summation of the SAW pulses. Mechanical displacements larger than 20 nm on a steel sample and 50 nm on aluminum were detected by a heterodyne optical interferometer. Examples of noncontact and nondestructive detection of thin surface breaking slots are presented.