NONLINEAR DIFFRACTION IN SPONTANEOUS 3-WAVE AND COHERENT 4-WAVE LIGHT-SCATTERING BY POLARITONS

Spontaneous three-wave and coherent four-wave scattering by polaritons in crystalline media with periodically modulated nonlinear quadratic susceptibility have been studied both theoretically and experimentally . Phase matching conditions and an expression for the scattering spect ral line shape with due account of cascade processes in nonlinear diff raction for coherent Stokes polariton light scattering have been deriv ed. Measurements of the light intensity distribution due to the three- and four-wave scattering in a LiNbO3:Nd:Mg crystal with a periodic dom ain structure are in good agreement with theoretical results. The pros pects for using the effects of nonlinear diffraction in spectroscopic studies of media with periodic distributions of nonlinear optical para meters, specifically, in precision measurements of the IR refractive i ndex dispersion and determination of the period and profile of the qua dratic susceptibility distribution are discussed. (C) 1997 American In stitute of Physics. [S1063-7761(97>00712-9].