Intensity controlled shaping of the beam profile using three-wave mixing in photorefractive Bi 12TiO 20

Abstract

In a degenerate forward three-wave mixing configuration with Bi 12TiO 20 (BTO) the gain in the signal wave is spatially controlled by choosing the intensity ratio between the two pump waves. Depending on this ratio the gain can be both positive and negative. For high pump intensities the gain does not dependent on the signal intensity itself. The phase distribution of the signal wave is not affected. The dependence of the signal wave gain on the pump intensity ratio is used for beam shaping with a BTO crystal (10×10×10 mm 3) at a wavelength λ=633 nm. An analytical solution for this dependence in three-wave mixing was found based on the coupled wave equations for two-wave mixing, neglecting optical activity and assuming small incidence angles. The analytical results show good agreement with experiments.