Four-wave scattering of light by coherently excited polaritons

An analysis was made of four-wave scattering of light by coherently excited phonon polaritons in homogeneous LiIO₃ and Mg:LiNbO₃ crystals, and also in periodically poled Nd:Mg:LiNbO₃. An investigation of lithium niobate crystals revealed a considerable discrepancy between the theoretically predicted and the experimentally determined dependences of the Stokes component intensity on the polariton phase mismatch. General expressions were derived for the line profile of the four-wave scattering in crystals with a periodic distribution of their nonlinear optical properties and in spatially confined nonlinear regions.