Influence of the polarization direction of two-beam coupling in photorefractive Bi12SiO20: Diffusion regime

Beam coupling effects in an optically active photorefractive crystal of Bi₁₂SiO₂₀ are very much influenced by the polarization direction of the interacting beams. Analytic expressions for the signal amplification in the diffusion regime have been derived for two commonly used crystallographic configurations,G<001> andG<110>,G being the grating vector. It is shown that only the <001> orientation is suitable for signal amplification. The results obtained for the diffusion regime can be applied, as a first approximation, to the more common and more intricate drift regime in which a bias electric field is applied to the crystal to enhance the coupling effect.