Abstract

Self-diffraction effects occur during the photorefractive grating recording process and thereby alter both the modulation depth and phase of the forming grating throughut the volume of the photorefractive medium. A method for calculating the polarization state evolution in photorefractive sillenite crystals (such as Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀) in the presence of such self-diffraction effects has been derived, and representative solutions have been studied. Self-diffraction effects are shown to alter the diffraction process remarkably. For the {K_G|| 〈001〉} orientation,¹ self-diffraction induces significant energy coupling gain; for the {K_G ⊥ 〈001〉} orientation, self-diffraction significantly modifies the polarization states, especially for Doppler-enhanced recording configurations. Striking spatial inhomogeneities are induced in the space-charge field, especially for the {K_G ⊥ 〈001〉} orientation, leading to striations in the space-charge field along the direction of propagation for the case of Doppler-enhanced recording and essentially constant amplitude but corrugated phase fronts for stationary recording. The diffraction properties of the two principal recording configurations prove to be distinctly different, and in part this difference is attributed to fundamental anisotropies inherent in the diffraction process. Finally, the degradation in energy coupling gain with increasing amounts of optical rotation ρd has been calculated for a few representative cases. This degradation can amount to of the order of 50% and must be considered in any holographically based measurements of effective electrooptic coefficients.

© 1988 Optical Society of America