Self-focusing of near-infrared laser beams in GaAs

Self-focusing of Q-switched Nd-YAG laser radiation in single-crystal GaAs has been studied. Near- and far-field intensity distributions measured after the light has passed through 1 cm of GaAs are given for various incident pulse energies. The self-focusing correlates qualitatively with linear absorption but is found to be most pronounced in p-type material. This self-focusing is believed to be of thermal origin, resulting from absorption coupled with a refractive index that increases with temperature.