Fraunhofer diffraction pattern of a Gaussian beam passing through a photorefractive crystal Bi₁₂GeO₂₀

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