DYNAMIC HOLOGRAPHY WITH NONPLANE WAVES IN SILLENITES

A three-dimensional model describing two-wave mixing in photorefractiv e crystals with finite beams of arbitrary shape is presented. The well -known longitudinal and transverse geometries are generalized by allow ing an arbitrary orientation of the local grating vector. The coupled equations for the wave amplitudes are solved numerically in the small- angle approximation by introducing the light paths as characteristics. The influence of amplitude distributions and phase-front curvatures a s well as the influence of geometrical arrangements and crystal proper ties (i.e. optical activity, externally applied voltage) on the energy exchange and the evolution of the polarization states is investigated . It is demonstrated that scanning the cross-section of the finite sig nal beam behind the crystal allows analysis of the coupling process in side the crystal which cannot be studied directly. The results of expe riments with finite beams carried out on a BSO crystal are in good agr eement with the numerical calculations.