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  -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/μs and attenuation of approximately 10 dB/(cm GHz2), 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.