2-SECONDARY-CENTER MODELING OF PHOTOREFRACTION AND COMPARISON WITH NANOSECOND PULSE ILLUMINATION EXPERIMENTS IN BARIUM-TITANATE

We report on the formation and subsequent dark evolution of induced ab sorption and photorefractive gratings produced by a high-intensity 15- ns pulse in an as-grown sample of BaTiO3, crystal. We show that the ex perimentally observed multiple time constants for decay of the induced absorption and buildup of the grating in the dark can be explained an d successfully simulated by a numerical model of photorefraction incor porating two secondary (hole-trapping) centers in addition to the deep level. The model also takes into account combined electron and hole p hotoconductivity and high-intensity illumination. We present a full de scription of the method of numerical solution of the zeroth (homogeneo us illumination) and the first-order parameters (inhomogeneous illumin ation) in this model regime for either steady-state or transient pulse trains and dark-evolution conditions. (C) 1998 Optical Society of Ame rica.