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Subject of study. The characteristics of the quasi-collinear acousto-optic diffraction geometry in a biaxial Tl3PSe4 crystal were investigated. Aim of study. This study aimed to obtain the characteristics of the Tl3PSe4 crystal that show the possibility and promise of developing quasi-collinear acousto-optical tunable filters in the infrared range of the spectrum. Method. The quasi-collinear acousto-optic diffraction in the Tl3PSe4 crystal was analyzed based on the coupled-wave method in combination with Fourier-optics methods. A covariant approach was used to calculate the phase and group velocities, and the components of the diffraction tensors of the interacting optical and ultrasonic beams. The parameters of the quasi-collinear acousto-optical tunable filters were estimated using well-known formulas generalized to the case of acousto-optic scattering in an optically biaxial medium. Main results. The anisotropy parameters of the shear acoustic mode utilized in the proposed acousto-optical tunable filters propagating in various directions of the YZ plane were calculated. For a wide range of cut angles of this facet plane, the mutual orientation of the acoustic and optical facets of an acousto-optical cell required for the practical implementation of the quasi-collinear diffraction regime was determined. The main characteristics of the quasi-collinear Tl3PSe4-based acousto-optical tunable filters were estimated. The effect of the incident optical beam divergence on the shape and width of their transmission function was studied. The most optimal variants of filters were revealed in terms of spectral resolution and power consumption. It has been established that these acousto-optical tunable filters significantly outperform the existing analogs in terms of angular aperture and energy efficiency. Practical significance. The variants of acousto-optical tunable filters proposed in this paper can be used for spectral analysis tasks in the wavelength range from 2 to 8 µm, which do not require an excessively high spectral resolution from the acousto-optical device.
Kupreychik et al. (Wed,) studied this question.