ИСТИНА

Development of devices operating not only in optical but also in infrared and ultraviolet ranges is the task of utmost importance in acousto-optics. Current work is devoted to examination of an acoustic field structure in a two-coordinate tellurium deflector. Calculations are carried out by the angular spectrum method in the given displacement approximation. A tellurium crystal have uniquely high figure acousto-optic figure of merit among other materials in the far infrared range. Other unique property of the tellurium monocrystal is a very strong anisotropy of acoustical properties. It causes complicate structure of acoustic field and strong dependence of the structure on crystal cut. In the current work we discuss results of calculations of acoustic intensity distribution. Acousto-optic cell with transducer in the XY and YZ planes is considered. Frequencies of signal were 15, 25, 35 and 22 MHz. Two cuts of crystal were analyzed. In the first cut facets were parallel to main crystal axis and in the second crystal was rotated in 5° around Z axis relative to first. Longitudinal piezoelectric transducer was used. Strong acoustic anisotropy leads to strong walk-off effect for relatively small cut angles and to beam divergence much more intensive comparatively to diffraction divergence. Moreover, near X tellurium axis there is fast rotation of polarization vector occurs which have strong influence on conditions of beam excitation. We show that there is one beam in cell with facets oriented along main crystal axis. This beam propagates in direction perpendicular to the facet. For the 5° cut there are three non-coplanar beams exists. We perform estimation of excitation efficiency of these beams excitation. Calculations for one plane wave show that longitudinal piezoelectric transducer in XZ plane excite two beams. One beam corresponds to one sheet of tellurium slowness surface. In the angular spectrum method acoustic field is a superposition of plane harmonic waves. Results of both methods are in good agreement with each other.