Number of reflecting layers as a dominating factor of the influence of an acoustic grating on the coherence degree of an optical field

The effect of two main regimes of the anisotropic Bragg acoustooptic (AO) diffraction on the coherence degree of an optical field from the point of view of the number of acoustic grating layers intersected by an optical beam is analysed. It is shown based on the AO interaction in a TeO₂ single crystal that despite a substantial difference (approximately by five times) between acoustic frequencies used in the regimes of large and small angles of light incidence with respect to the acoustic wave front, the character of the speckle pattern is almost the same.