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Abstract. We have analyzed a gradient piezogyration effect induced by torsion stresses in optical materials belonging to different point groups of symmetry. It has been shown that the effect manifests itself as a rotation of light polarization plane only in the tetragonal and cubic crystals and textures described by the point symmetry groups / / mmm   , mm  , / m  , 4/m, 4/mmm, m3 and m3m, provided that light propagates along the optic axis in the tetragonal crystals, along one of the crystallographic axes in the cubic crystals, or along the infinity fold axis in the textures and the crystals are twisted around these axes.Keywords: torsion stresses, optical activity, gradient piezogyration PACS: 78.20.Ek, 78.20.hb, 45.20.da UDC: 535.56+535.012+53.082.12+535.55As shown in our recent studies [1-3], a torsion stress-induced optical activity is the effect caused by spatial derivatives of mechanical stresses rather than by the stresses themselves. It is described by the tensorial relationwhere ln g  is the induced increment of the gyration tensor, / km v X    the coordinate derivative of the stress tensor, and lnkmv  a fifth-rank axial tensor. Notice that the lnkmv  tensor has nonzero components even in centrosymmetric media. As a result, generation of spatially inhomogeneous distribution of mechanical stress tensor components in such media would lead to appearance of optical rotation. It is this property that distinguishes the gradient piezogyration effect from a commonly known piezogyration [4][5][6][7] described by the formulawith lnkm  being the fourth-rank axial piezogyration tensor equal to zero for any centrosymmetric media. Comparing Eqs. (1) and (2), one can see that the gradient piezogyration appears alone, without a usual accompanying piezogyration effect, in centrosymmetric materials since the piezogyration is symmetry forbidden here. It has been shown in Refs. [1][2][3] that it would be convenient to study the gradient piezogyration under crystal torsion, because the torsion moments can be successfully controllable unlike, e.g., residual internal inhomogeneous stresses.From the other hand, it is known that the shear stress tensor components 31  and 32  induced by the torque moment Z M are described by the relation [8]

Abstract. We have shown that residual stresses existing in isotropic glass media lead to appearance of polarisation singularities of optical wave front. These singularities are characterised by the strength of topological defect equal to 1/ 2  and should lead to the appearance of optical vortices with the topological charge 1  . Annealing of the samples has led to annihilation of the polarisation singularities, homogenisation of spatial distribution of the phase difference and zeroing of the latter, thus suggesting disappearance of the residual stresses. The role of the singularities revealed in solving the known problem of 3D stress tensor field reconstruction is discussed.

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