Anisotropy of piezo-optic and elasto-optic effects in langasite family crystals

Abstract The surfaces of the photoelasticity effects spatial distribution are constructed for langasite (LGS) and catangasite (CTGS) crystals basing on the matrices of piezo-optic and elastic-optic coefficients (POC and ELOC). It is shown that the maxima of the longitudinal piezo-optic effect (POE) are commensurate for both crystals and correspond to POC π33; the maximum value of transverse POE (vectors of uniaxial pressure and light wave polarization are mutually perpendicular) in CTGS crystals is almost two times higher comparing to LGS. The maxima of the transverse elastic-optic effect (ELOE) are also significantly higher in CTGS. It should be emphasized that the maxima of the surfaces of the transverse POE are not located on crystallographic axes, but correspond to the directions that are shifted for 13 … 33° from optical axis of the crystals. Thus, the angle between maximum ELOE and optical axis in CTGS equals 13°. The maximum values of POE, ELOE and the directions of the maxima were determined analytically using the method of partial derivatives. The acousto-optic figure of merit M2 was determined for the ELOE maxima. It has been shown that this value is two times higher for CTGS, comparing with LGS. The first attempt to make the correlation between the POE, ELOE maxima and structural properties of these crystals has been carries out.