Multichannel TeO2 Bragg cells: reduction of the ultrasonic diffraction

In many acoustooptic applications where multichannel Bragg cells are required, the performances are limited by the spreading of the acoustic waves propagating in the medium. This phenomenon is particularly obvious when Paratellurite (TeO₂) is utilized. In this paper, the diffraction of the slow shear wave is evaluated. It is shown that an angular tilt θ of the acoustic wavevector from the [110] axis in the (001) plane allows to greatly reduce acoustic beam diffraction. Experimental validation is then described: a Schlieren image of a multichannel TeO₂ Bragg cell shows the propagation of different acoustic waves with θ=5°. Ultrasonic diffraction is significantly reduced and the theoretical predictions are well confirmed