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An acousto-optic tunable filter (AOTF) based on a paratellurite crystal for tuning the radiation wavelength of a copper vapor laser has been calculated and manufactured. The geometry of acousto-optic interaction in AOTF for performing wide-angle spectral-selective diffraction is based on the parallelism of the incident and diffracted light tangents to the wave surfaces. The system of equations for the above conditions is solved and the maximum numerical aperture of the filter in the scattering plane is determined. It has been found that the required angle of deviation of the acoustic wave vector from the [110] direction leads, due to the large elastic anisotropy of paratellurite, to a significant deviation of the group velocity vector, or energy flux. This angle between the vectors of the phase and group velocities can be tens of degrees, which makes it necessary to manufacture an acousto-optic cell of a special shape. In addition, when deviating from the [110] direction, this also leads to a change in the velocity of elastic waves, in this case to its increase and, as a result, to a decrease in the efficiency of acousto-optic interaction. It is calculated that the maximum numerical aperture in the diffraction plane is obtained at an angle of deviation of the elastic wave vector from the [110] direction by approximately 18 degrees. In this case, the numerical aperture in the diffraction plane is almost twice the numerical aperture in the orthogonal plane. Therefore, for the case of the same numerical aperture, it is sufficient to choose an angle of about 10 degrees. The paper presents a mathematical description and calculation results for the main characteristics of an acousto-optic tunable filter. Based on the performed studies, an acousto-optic tunable filter for controlling the parameters of a copper vapor laser at two radiation wavelengths λ1 = 510.6 nm and λ2 = 578.2 nm was fabricated and experimentally investigated.
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