The fundamental possibility of using the acoustooptic (AO) Bragg diffraction in problems of a frequency shift of a speckle-containing optical field both with and without field filtering for removing fine-grain background has been demonstrated. Two regimes of anisotropic diffraction observed in a TeO_2 uniaxial crystal, when optical rays propagate close to the crystal optical axis (I) and far from it (II), have been studied. Experiments performed on the basis of an acoustooptical cell made of TeO_2, in which speckle-containing optical radiation at a wavelength of 0.63 μm and an average speckle size of 50-70 μm diffracted at a slow traveling acoustic wave at a frequency of 44 MHz, demonstrated the absence of radiation filtering in diffraction regime I and enlargement of the average speckle size to 220-280 μm in regime II resulting from diffraction.
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