T. G. Golovina

Experimental and theoretical determination of the optical rotation in langasite family crystals

Optical properties of 21 langasite family crystals of different compositions have been studied. Dispersion dependences of the specific optical rotation for light propagation along the optical axis are experimentally obtained for La3Ta0.25Ga5.25Si0.5O14, La3Ta0.25Zr0.5Ga5.25O14, and La3Zr0.5Ga5Si0.5O14 crystals. Based on the known refractive indices of six crystals, the refractive indices for 15 crystals are calculated by the method of molecular refraction. Based on the experimental data, the dependence of the specific optical rotation for light propagation along the optical axis on the birefringence is plotted for 10 crystals. Using this dependence, the specific optical rotation is estimated for 11 more crystals of different compositions. Based on X-ray diffraction data, the specific optical rotation is calculated by the WinOptAct program for 13 crystals. The application of different methods makes it possible to predict the optical characteristics of langasite family crystals of different compositions.

Gyrotropic Absorbing Crystals of Lower Symmetries

The specific features of polarization of natural waves propagating in crystals near their optical axes have been studied successively in transparent gyrotropic, absorbing, and gyrotropic absorbing crystals of classes 222, 2, 1, m, and mm2. The dependences of the ellipticities of natural waves and the azimuth of polarization of light transmitted through a crystalline plate (the case of normal incidence) on the orientation of the optical-axis plane of the plate axes with respect to the normal to surface are calculated for these crystals. These characteristics are compared for crystals of axial and planal classes with two different orientations of the optical-axis plane with respect to the symmetry elements of crystal.

On the structural basis of the presence of two optical axes in α-HIO3 crystal

An X-ray diffraction study of α-HIO3 crystal has been performed with the following results: sp. gr. P212121, Z = 4, a = 5.5360(3) Å, b = 5.8723(6) Å, c = 7.7291(5) Å, and R factors R(F)/wR(F) = 0.86/0.69%. Disordering of iodine site is revealed, which is described in terms of anharmonic atomic displacements. Packing (likely unique) of all structure atoms over two systems of planes rotated by an angle close to the rotation of optical axes (47°) is revealed. The rotation of the plane of polarization of light based on the structural data is calculated for the first time for the α-HIO3 crystal.

Specific features of optical activity in various uniaxial crystals

The influence of the antisymmetric part of the gyration pseudotensor on the characteristics of reflected and transmitted light has been considered for crystals of classes 3, 4, and 6. The results are compared with the corresponding data for crystals of classes 32, 422, and 622 with a symmetric gyration pseudotensor. Specific features of the optical activity in crystals of classes 3m, 4mm, and 6mm with an antisymmetric gyration pseudotensor have been studied. Crystals of classes

Optical axes in various absorbing crystals

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Anisotropy of Optical Activity in Langasite Family Crystals

and

Manifestation of optical activity at oblique incidence of light in crystals of classes

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