We show that the inclusion of the longitudinal component of the induced space-charge electrostatic field during two-beam coupling in a diffusion-dominated photorefractive material such as barium titanate with mismatched boundary conditions can predict enhancement of the higher-order diffraction efficiency, thereby reducing the minimum initial two-beam coupling ratio required for higher-order generation. We perform the analysis using the exact Kukhtarev equations and a rigorous coupled-wave diffraction theory. Expressions for the induced optical permittivity tensor including the presence of the longitudinal field are provided.
© 1996 Optical Society of America
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