Potentials of the acousto-optical spectral data processing on a basis of a novel algorithm of the collinear wave heterodyning in a large-aperture KRS-5 crystalline cell

Recently proposed modern technique of a precise spectrum analysis within an algorithm of the collinear wave heterodyning implies a two-stage integrated processing, namely, the wave heterodyning of a signal in a square-law nonlinear medium and then the optical processing in the same cell. Technical advantage of this approach is in providing a direct processing of ultra-high-frequency radio-wave signals with essentially improved frequency resolution. This algorithm can be realized on a basis of various physical principles, and we consider an opportunity of involving the potentials of modern acousto-optics for these purposes. From this viewpoint, one needs a large-aperture effective acousto-optical cell, which operates in the Bragg regime and performs the ultra-high-frequency co-directional collinear acoustic wave heterodyning. The technique under consideration imposes specific requirements on the cell's material, namely, a high optical quality of large-size crystalline boules, high-efficient acousto-optical and acoustic interactions, and low group velocity of acoustic waves together with square-low dispersive acoustic losses. We focus our attention on the solid solutions of thallium chalcogenides and take the TlBr-TlI (thallium bromine - thallium iodine) solution, which forms KRS-5 cubic-symmetry crystals with the mass-ratio 58% of TlBr to 42% of TlI. Analysis shows that the acousto-optical cell made of a KRS-5 crystal oriented along the [111] -axis and the corresponding longitudinal elastic mode for producing the dynamic diffractive grating in that crystal can be exploited. With the acoustic velocity of about 1.92 mm/mu s and attenuation of approximately 10 dB/(cm GHz(2)), similar cell is capable to provide an optical aperture of 50 mm and one of the highest figures of acousto-optical merit in solid states in the visible range. Such a cell is rather desirable for applications to direct parallel multi-channel optical spectrum analysis with substantially improved frequency resolution.