Laser-induced transient stress field studied by time-resolved photoelasticity technique

Abstract

Interaction between an intense laser pulse and a material is a key issue to understand and control photo-induced processes. It is, however, rather difficult to study the interaction in detail because it occurs in a very narrow area and a very short period. In addition, it is usually accompanied by plasma formation, which causes difficulties for the most of observation and measurement techniques. We have developed a time-resolved imaging technique which uses a pulse laser as a probe light and an ICCD camera as a recording devise, and successfully observed the dynamical change of the spatial distribution of laser induced transient stress fields by both shadowgraph and photoelasticity images using transparent materials. Recently, we have found that photoelasticity imaging of epoxy-resin observed under water provide clear images which allow us the semi-quantitative estimation of the magnitude of laser induced stress. We can make the semi-quantitative estimation of the laser-induced stress by comparing images to those obtained for designated pulse energies. Effect of surface roughness is examined. The effect of the confinement of laser ablation by water is shown semi-quantitatively. The interaction of laser to the metal surfaces is examined by using epoxy samples the surfaces of which are coated by several metals. Transient stress induced in inside of the bulk materials by focusing the laser at inside of transparent materials are dynamically observed and compared with permanent damages induced by the laser irradiation.