Self-rotation of the path of a doubly Gaussian speckle beam in photorefractive crystals

An analytical solution is given of the propagation of a doubly Gaussian speckle beam in photorefractive crystals. A beam which retains the Gaussian profile of the angular spectrum and of the envelope of the speckle structure in a transverse cross section exhibits self-rotation of its path at a rate proportional to the square of the irregular ('grey') divergence. The bulk of the beam self-rotation takes place within a distance equal to its focal waist.