Influence of wet surface condition on the propagation behavior of laser-generated ultrasound

It is known that the efficiency of generating laser ultrasound is greatly enhanced by moisturizing the surface with water or oil. Although this is a common technique used in practice, the physical behavior under such condition is not well understood. This paper deals with a theoretical model to study the influence of the wet surface condition on the behavior of wave propagation. The solutions for both longitudinal and shear waves are obtained using the Fourier analysis and evaluating the transform integral asymptotically. This model, developed by assuming an elliptical distribution of normal surface tractions over the illuminated source area, can predict the directivity patterns. Both circular and line focused source beams are considered. The theory was evidenced by the experimental study, in which the effects of the most influential parameters such as beam diameter and frequency of the propagating wave are investigated. The experimental results are in excellent agreement with the theoretical predictions....