Biaxial AOTF transfer functions for spatial image filtering

Biaxial crystals offer a huge advantage for design of acousto-optic tunable filters (AOTFs) because of a variety of two-dimensional transfer functions. Special configurations of noncritical phase matching of anisotropic Bragg diffraction offer the transfer functions suitable for tunable spatial filtering of laser beams, which can be used for phase imaging and laser beam shaping. We analyze special configurations of AOTFs in alpha-iodic acid (orthorhombic system) and potassium yttrium tungstate (monoclinic system) crystals and demonstrate unique two-dimensional transfer functions, which originate from symmetries of the biaxial crystals' refractive index surface. The results include transfer function simulations and corresponding configuration analysis for AOTF design.