Spatial anisotropy of the acousto-optical efficiency in lithium niobate crystals

Abstract

We report the spatial anisotropy of the acousto-optic (AO) figure of merit M2 in LiNbO3 crystals. The analysis is based on the indicative surfaces being calculated for several geometries of the AO diffraction. Basing on these results the most efficient geometries of AO cells made of LiNbO3 crystals are determined. It is revealed that the cells made of certain nondirect crystal cuts provide several times better AO diffraction efficiency comparing to the traditional ones, i.e., made of direct cuts of LiNbO3. The obtained results present considerable practical interest since may be useful in a designing of highly efficient AO cells made of LiNbO3 crystals. The methodology developed in the present work may be applied to other crystal materials as well.

Anisotropic diffraction of bulk acoustic wave beams in lithium niobate

“…This mode is non-piezoactive unlike the other two modes propagating in the same plane, and its phase velocity can be expressed as where c 44 , c 66 and c 14 are the elastic stiffness constants and q is the crystal density. Orthogonal anisotropic AO diffraction in YZ plane by the pure shear wave has a maximum of figure of merit M 2 = 15.9 Â 10 À18 s 3 /g [3,4]. That value is high enough for practical design of AO devices, namely 8 times higher than in crystalline quartz, that inspires the search for efficient AO diffraction in other configurations in this plane, e.g.…”

“…Elastic, photoelastic and piezoelectric properties of lithium niobate were studied comprehensively [1][2][3][4]. Due to strong piezoelectric effect in this material, SAW and surface skimming BAWs can be generated by an interdigital transducer located on the crystal surface.…”

Anisotropy of the acousto-optic figure of merit for LiNbO_3 crystals: isotropic diffraction

“…For example, the attempts at the analyses of AOFM anisotropy for the LiNbO 3 crystals have been made in the works [14,15]. However, the technique suggested in those studies is not transparent enough, since it is not clear how to use it in practice, the results of Refs.…”

“…Finally, the authors of the mentioned works have not presented the relations for the effective elastooptic coefficients (EECs). These makes the papers [14,15] completely wrong and inappropriate for further discussion. Interesting and reliable results for the AOFM anisotropy in lithium niobate have been obtained in Ref.…”

“…However, the technique suggested in those studies is not transparent enough, since it is not clear how to use it in practice, the results of Refs. [14,15] are based on the incorrect assumption that one can determine the AOFM anisotropy by merely rewriting the elastooptic tensor in some rotated coordinate system. In addition, authors [14,15] have considered only wave vectors but not all tensors in the spherical coordinate system; the Bragg condition is not satisfied, in particular for those interactions which lead to the extreme values of AOFM; formula for AOFM which take into account the acoustic and optical beams oblique propagation has not relation to this effect (see [11]).…”