Erasure of holographic gratings in photorefractive materials with two active species

The erasure kinetics of holographic gratings has been theoretically studied for a material containing two photorefractive species. The approach is an extension of the method developed by Carrascosa and Agullo- Lopez for a simple photorefractive center. The erasure of the grating involves the transfer of electronic charge between the two photorefractive systems together with a spatial transport of the charge. Both processes may have, in general, comparable time constants leading to a more complicated formalism than that for a single species. The electronic exchange between two photoactive centers has been first solved analytically. Then, the erasure kinetics of a sinusoidal grating, including charge exchange, has been formulated under the short transport length approximation. The coupled equations governing the decay of grating amplitude and the velocity of fringes have been numerically solved (a) after neglecting diffusion and (b) in the general case. The solution for the time dependence of grating amplitude is nonexponential. The particular situation where the electronic exchange process is very fast in comparison to grating erasure has been solved assuming arbitrary transport lengths. The decay of grating amplitude consists of two exponential curves if the photovoltaic drift is ignored and it is nonexponential if it is included. For short transport lengths, the decay reduces to a single exponential.