INTENSITY CONTROLLED SHAPING OF THE BEAM PROFILE USING 3-WAVE MIXING IN PHOTOREFRACTIVE BI12TIO20

In a degenerate forward three-wave mixing configuration with Bi12TiO20 (BTO) the gain in the signal wave is spatially controlled by choosing the intensity ratio between the two pump waves. Depending on this rat io the gain can be both positive and negative. For high pump intensiti es the gain does not dependent on the signal intensity itself. The pha se distribution of the signal wave is not affected. The dependence of the signal wave gain on the pump intensity ratio is used for beam shap ing with a BTO crystal (10 x 10 x 10 mm(3)) at a wavelength lambda = 6 33 nm. An analytical solution for this dependence in three-wave mixing was found based on the coupled wave equations for two-wave mixing, ne glecting optical activity and assuming small incidence angles. The ana lytical results show good agreement with experiments. (C) 1998 Elsevie r Science B.V. All rights reserved.