Abstract

We present a model which describes phase matching in an arbitrary biaxial acoustooptic tunable filter covering uniaxial crystals as a particular case. The model, in which we compute the exact momentum mismatch of the interaction, was applied to the calculation of the angular aperture (defined as the −3-dB contour of the input acceptance surface). This calculation was carried out in a general way, both from a crystal and interaction geometry point of view (uniaxial/biaxial, collinear/noncollinear). The results show interesting aperture features, e.g., a strong anisotropy, for certain ranges of values of the polar incidence angle. These features are shown to be associated with a sign reversal of the momentum mismatch, which allows the polar incidence angle to be changed over a significant range before the mismatch rises significantly in absolute value. Computer calculations are presented for uniaxial TAS at 10.6 μm and varying crystal lengths for simplicity. This model extends previous studies,¹ clarifying the operation of a general AOTF and providing design guidelines for actual devices.

© 1987 Optical Society of America