Erase rates in photorefractive materials with two photoactive species

Abstract

Erase rates for uniformly illuminated refractive-index gratings are derived for a model of photorefractivity in which two photoactive ions participate as donors and acceptors. The model leads naturally to decay of gratings at two separate rates. In some conditions the amplitudes of the components that decay at each rate are nearly equal, while the rates are substantially different. These conditions should be readily observable in crystals with two photoactive species. In other conditions, one amplitude greatly exceeds the other or the time constants are nearly equal, and a single rate would be observed. The ratios of the rates and amplitudes are insensitive to erase irradiance but very sensitive to grating period and absorption cross section. Illustrative parameters for Bi₁₂SiO₂₀ suggest that if two photoactive species are present, two decay rates should be observable.