Behavior of laser-induced ultrasonic waves radiated from a wet surface. Part II. Experimental work

The theoretical model presented in Part I of this article is experimentally verified using a Nd:YAG pulsed laser as a source to illuminate a wet surface. The longitudinal and shear directivities are determined from the displacements measured experimentally using a laser interferometer or a piezopolymer transducer. The experiments are carried out for circular sources of various beam diameters at two frequencies, in which the results are in good agreement with the theoretical predictions. The differences between this model and the conventional model are discussed by comparing the directivities and observing the influences of source beam size, frequency, and the source intensity. It is confirmed that the elliptical loading model predicts the behavior more accurately than the constant loading model, especially for larger laser beams operating in a high frequency regime.