Effects of spatial coherence on photorefractive two-beam coupling

Photorefractive two-beam coupling with partially coherent light is investigated both theoretically and experimentally. By applying partial-coherence theory, a spatially varying distribution function for the grating visibility is found analytically. For certain beam configurations, this function may be approximated as one-dimensional and the coupled wave equations may be established and solved numerically. When compared to the case of perfect coherence, partial coherence has two major effects on the beam coupling. One is that the effective grating length may be smaller than the crystal length as a result of the spatial-coherence limit. The second is that the visibility distribution over the grating is smaller than the constant visibility of the coherent case.