Modulation Instability of Low-Amplitude Quasi-Plane-Wave Optical Beams in Biased Photorefractive Crystals

We present a study of the modulation instability of low-amplitude broad optical beams in biased photorefractive crystals under steady-state conditions. The modulation instability growth rate can be obtained provided that E₀ is positive quantity, where E₀ is the field constant correlated with terms in the space-charge field .Our analysis indicates that the growth rates depend on E₀ and the ratio of the optical beam´s intensity to that of the dark irradiance, and the maximum modulation instability gain as well as the corresponding spatial-frequency increase with increasing E₀ and the ratio of the optical beam´s intensity to that of the dark irradiance. Relevant examples are provided where the photorefractive crystal is assumed to be of strontium barium niobate type.