Fraunhofer diffraction pattern of a Gaussian beam passing through a photorefractive crystal Bi 12 GeO 20

In this theoretical–experimental study, we use the Fresnel–Kirchhoff diffraction theory to simulate the formation of the far-field diffraction pattern of a divergent Gaussian beam propagated through a photorefractive crystal Bi 12 GeO 20 (BGO). We show that for the BGO, in addition to the wavefront curvature and change in the refractive index of the medium due to light intensity, there is a third contribution affecting the medium-induced nonlinear phase shift; the latter is related to the additional change in the refractive index produced by the photorefractive nature effect. We consider that this work contributes to the characterization of photorefractive materials using diffraction patterns.