Topological evolution of acousto-optic transfer functions in biaxial crystals

Modern applications of acousto-optic tunable filters (AOTFs) range from hyperspectral imaging in space research and biomedical optics to optical manipulation and ultrafast laser pulse shaping. The design of all AOTFs is based on optical anisotropy of crystals; until now, however, only uniaxial crystals have been used. Lower symmetry and outstanding acousto-optic (AO) properties of some new biaxial crystals make them promising candidates for quali-tative improvements in this field. Anisotropic AO interaction in crystals allows angular noncritical phase-matching (NPM) configurations that are commonly used in different AOTF types. In this work, we perform a comprehensive geometrical and topological analysis of 2D transfer functions of AO interaction under NPM condition in biaxial crystals. The topological classification of the 2D transfer functions under an angular NPM condition is proposed. In principle, in the planes of a biaxial, the same types of transfer function exist as in uniaxial crystals, including cross-like topology of collinear diffraction, circular topology, and ultrawide angle topology. In addition, new topological types of the AO 2D transfer function are reported, which exist only in biaxial crystals.(c) 2022 Optica Publishing Group