Reflection of an optical beam having speckles from a "thick" acoustic grating

A substantial change in the spatial coherence of an optical field with a speckle pattern was experimentally observed during reflection of the field from a "thick" Bragg grating. This effect is explained within the framework of the Gauss – Sheel model by the difference in the diffraction efficiencies of individual regions of the field represented by Gaussian beams with different angular divergences.