Method of extreme surfaces for optimizing geometry of acousto-optic interactions in crystalline materials: Example of LiNbO3 crystals

Abstract

We suggest a method for optimizing geometry of acousto-optic (AO) interactions in anisotropic crystalline materials. Within the framework of this method, one gets global maximums of AO figure of merit M2 and their spatial orientations, proceeding from so-called “extreme” indicative surfaces, which are obtained after finding such an acoustic wave propagation direction that maximizes the M2 parameter for each propagation direction of the incident electromagnetic wave. The method improves earlier indicative surface-based techniques in several aspects, particularly in properly accounting for the momentum conservation condition for the AO diffraction, and yields a higher accuracy in assessing spatial anisotropy of the AO effect. We have constructed the extreme surfaces of LiNbO3 crystals for all possible cases, including those of isotropic/anisotropic AO diffractions and longitudinal/transverse acoustic waves. The anisotropy of the AO figure of merit for LiNbO3 is analyzed for the acoustic frequencies 0.01–2.0 GHz and the light wavelengths 405–1444 nm. The absolute M2 maximums refer to ‘indirect crystal cuts' and are equal to 26.3 × 10−15 s3/kg at 2 GHz and 405 nm, and 15.4 × 10−15 s3/kg at 0.4 GHz and 1444 nm.

Anisotropy of acoustooptic figure of merit for TeO2 crystals. 1. Isotropic diffraction

“…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 lith-ium niobate have been obtained in Ref.…”

New Method to Calculate Spatial Distribution of Acousto-Optic Figure of Merit in Crystals

“…The maximal magnitude of M 2 for the diraction from ordinary to ordinary light wave is close to the magnitude known from the article [9].…”

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]).…”