Collinear acousto-optic filtering of divergent optical beams in the presence of optoelectronic feedback

The divergence of a diffracting light beam affects the characteristics of acousto-optic (AO) interaction. This is due to the side components of the optical beam spatial spectrum propagating in the crystal along the directions different from the beam axis. The divergence causes the AO diffraction efficiency decrease and the distortion of the AO device transmission function - its bandwidth increases and the side lobes are smoothed. We suggest the method to compensate the optical beam effect on the collinear AO diffraction transmission functions shape based on optoelectronic feedback circuit application connecting the AO cell optical output and its piezoelectric transducer. It is shown that such method makes it possible to narrow the transmission function passband and increase the spectral contrast of the system. It is found out that feedback does not affect the AO diffraction transfer functions. Thus, the introduction of feedback makes it possible to increase the spectral resolution of AO devices without compromising the AO device angular aperture.