Propagation of ultrasonic beams in paratellurite crystal.

Analytical expressions have been obtained of the main curvatures of the concavity of the wave vector surface, corresponding to the quasi-transverse wave, versus anisotropy parameter C = C11-C12-2C66 of the paratellurite crystal. Changes in the form of the sound beam on scanning in the direction of its propagation in the (001) and (110) planes have been investigated. It has been found that near the acoustic axis lying in (001) considerable transformation of the beam takes place; initially extended, it becomes squeezed along the [001] axis. The conditions for focusing and channelling of ultrasound radiation have been determined. The propagation directions at which anisotropy of the paratellurite crystal does not influence the beam divergence have been found. It is shown that, for a wide range of deviation angles theta of the wave normal from the [001] axis in the symmetry plane (110) (theta < or = 50 degrees), the presence of anisotropy leads to weaker diffraction broadening. The character of variation in the direction and divergence of the sound beam on scanning in the vicinity of the [110] direction has been studied experimentally.