Computer model for transient grating experiments and its application to analysis ofLiTaO3s

A computer program is used to model transient grating experiments where two laser pulses induce a transient response in the sample and the time evolution of that response is monitored by the diffraction of a third pulse. The program is designed so that experimental conditions such as spot sizes, excitation angle, probe angle, relative pump and probe positions, and laser wavelength can be readily varied. The model accommodates acoustic and polariton excitations which travel significant distances during an experiment. This program is used to simulate and analyze transient grating experiments of ${\mathrm{A}}_1$ -symmetry polaritons in the ferroelectric crystal ${\mathrm{LiTaO}}_3$ . Previous experiments have used two different detection schemes for the scattered pulse, and two different models for the optic modes of ${\mathrm{LiTaO}}_3$ were proposed. The simulations show that the discrepancies result from an experimental artifact in the heterodyne detection experiments, and both sets of experiments are consistent with one model for the crystal's optic modes.