Intensity-dependent absorption and photorefractive effects in barium titanate

We present experimental data for BaTiO3 that exhibit an intensity dependence in the absorption coefficient and the two-beam coupling coefficient at intensities between 0.002 and 40 W/cm2. The effective empty-trap concentration was found to increase with intensity. We present a model, in the spirit of commonly used (photorefractive) theories, for photorefraction and optical absorption that explains these effects. The intensity dependence was attributed to the presence of secondary photorefractive centers.