<title>Transient stress field in a sample induced by intense laser pulses</title>

Abstract

We report on dynamical observation about interaction of the fundamental radiation from a Q-switched Nd:YAG laser to the surface of PMMA observed by an imaging system with nanosecond time resolution, with special emphasis on stress waves inside the sample. We observed stress wave which propagated into the material and a pressure wave propagated into the atmosphere by shadowgraph and photoelastic methods. In the shadowgraph images, a shadow corresponded to the longitudinal elastic wave was clearly observed in the bulk. In photoelasticity images, another contrast which should correspond to the transverse wave was also observed. The contrast ofthe photoelasticity images depended on laser pulse energy. The contrast and thus the amount of absorbed energy were affected by the surface roughness: roughness greater than 1 micrometer caused complete absorption of laser energy at the surface. Based on this result, we try to examine the effects of incidence angle of the laser to coupling between laser radiations and the material.