Control of material properties by parallel laser irradiations at multiple laser spots using a spatial light modulator

Abstract

Applications of the parallel fs laser processing system to spatial control of material properties are presented. In the parallel laser processing system, multiple light spots are generated by modulating the spatial phase distribution of a laser beam with a spatial light modulator. When the light spots are sufficiently separated from each other or the energies of the excitation laser pulses are weak, there is little interaction between photoexcited regions. In many cases, no interaction between each photoexcited regions is preferable, because thermal energies and stresses from each photoexcited regions could influence the processing accuracy. On the other hand, we found that the interaction of thermal energies and transient stresses in a parallel laser processing inside transparent materials can be used for controlling the spatial distributions of material properties. In this paper, we show two applications of the interactions between multiple photoexcited regions. One is the control of the shape of the heat modification and distributions of elements inside glasses. Another is the modification of dislocation bands inside rock-salt crystals by the interference of stress waves generated at multiple spots.