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 surfa ce. The longitudinal and shear directivities are determined from the displa cements measured experimentally using a laser interferometer or a piezopoly mer transducer. The experiments are carried out for circular sources of var ious beam diameters at two frequencies, in which the results are in good ag reement with the theoretical predictions. The differences between this mode l and the conventional model are discussed by comparing the directivities a nd observing the influences of source beam size, frequency, and the source intensity. It is confirmed that the elliptical loading model predicts the b ehavior more accurately than the constant loading model, especially for lar ger laser beams operating in a high frequency regime. (C) 2001 American Ins titute of Physics.