Optical Detection of Transient Lamb Waves on Rough Surfaces by a Phase-Conjugate Method

Abstract

A convenient method is described for optically detecting Lamb waves on rough surfaces. A pulsed YAG laser excites Lamb waves, which are detected in a noncontact manner by a Michelson interferometer with a self-pumped phase-conjugate mirror. The present method automatically corrects the wavefront distortion caused by rough surfaces and also shows a flat spectral response over large bandwidths necessary for the analysis of the dispersion relationship. To illustrate the validity of the method, experimental results are presented for two kinds of thin plates.