New parametric scattering in photorefractive Sr0.61Ba0.39Nb2O6:Cr

A new class of light-induced parametric scattering, not included in the conventional model, has been discovered in photorefractive Sr(0.61)Ba(0.39)Nb(2)O(6):Cr illuminated by two coherent beams. A novel model of multiwave mixing of coherent noise and transmitted light is developed to explain the new scattering phenomena. The model includes all known types and predicts a multitude of new types of parametric scattering. Generalized phase-matching conditions for parametric scattering in photorefractive crystals are proposed.