The paper is devoted to analysis of regular trends and peculiarities of optical image processing by means of tunable acousto-optic filters. One of the goals of the investigation was to determine basic reasons limiting spatial resolution in acousto-optically processed images. As found, the limitations originate from laws of Bragg acousto-optic interactions in birefringent crystals. A case of the wide angle geometry of light diffraction was examined for the single crystal of paratellurite. It is shown that optical quality of the processed images depend on such interaction characteristics as mutual directions of propagation of optic and acoustic waves in the crystal, on dimensions of piezoelectric transducers launching acoustic waves in TeO2, on optical wavelength and also on linear and angle apertures of optical beams. It is proved in the paper that the spatial resolution during the acousto-optic imaging depends on all these factors in a very complicated manner so that selection of an optimal cut of the birefringent crystal occurs not simple and evident. A trade-off between the spatial resolution and the optical throughput of the imaging device at various optical wavelengths is required. A detailed consideration of the problem becomes necessary depending on a particular problem to be solved by the acousto-optic filter. General methods to design the acousto-optic imaging devices operating in the ultraviolet, visible and infrared regions of spectrum are also discussed in the presentation.
The paper is devoted to the theoretical and experimental investigation of spatial resolution of images obtained during acousto-optic spectral filtration. The consideration was carried out for a wide angle acousto-optic filter designed on the base of paratellurite single crystal. The crystal was cut in the (1 1 0) plane with the direction of acoustic wave propagation at the angle 10 ° relative to the axis . It was found that optical quality of a filtered image is influenced by a spectral bandwidth of a filter. The spectral bandwidth is determined by a length of piezoelectric transducer that generates ultrasonic waves in an acousto-optic cell. The dependence of a number of resolvable spots on the piezotransducer length was examined theoretically. It was shown that a wavelength of the filtered radiation influences the quality of the processed image. Precise and approximate equations have been derived to determine the spectral passband of the acousto-optic filer, the angular field of view of a single pixel, the angular aperture of the device and the number of resolvable spots in a line. Resolution of the images obtained during the acousto-optic filtration was also measured in the experiment.