A number of designs have been proposed for acousto-optic deflectors th
at use anisotropic acousto-optic diffraction in TeO2. The interaction
geometries commonly used permit acceptable deflection angles by ensuri
ng that, to first order, the required angle of incidence of the optica
l beam is fixed. For these interaction geometries, a complicated relat
ionship between the deflection angle and the acoustic frequency is pre
dicted. However, a simple linear relationship is observed experimental
ly. It is shown that this discrepancy is due to the angular spread in
the acoustic beam, which is necessary for the operation of a practical
acousto-optic deflector.