Kostyrko M. Birefringence and gyrotropy of LiNbO3 and NaBi(MoO4)2 crystals at axial-tensor deformations

The influence of complex external fields on the optical indicatrix orientation was analyzed. On the base of description of turns as axial vectors was shown that the turn of optical indicatrix around third crystallophysical axis allways will exist at the existance of its turns around two another crystallophysical axes. The expression for the turn of optical indicatrix around third crystallophysical axis was received. It was established that deformation of twisting and bending may be described by axial tensor of second rank. On the base of optical indicatrix equations and simplificated description of twisting by axial tensor of second rank the gradient piezooptical effect induced by twisting strains had been analyzed for crystals of akll symmetry point groups. The influence of twisting deformation on the orientation of optical indicatrix was experimentally investigated for LiNbO3 crystals. On the distribution of optical indicatrix in XY-cut of LiNbO3 crystals at twisting around Z axis we detected jointing of different regions of crystals with interchanged axes X and Y induced by twisting. At twisting around X axis and light propagation along Z axis the turn of optical indicatrix was detected equal to 45° in XY-cut of LiNbO3 crystals. It was shown that experimental results are in accordance with phenomenological analysis. The influence of twisting deformation on the birefringence of LiNbO3 crystals was experimentally investigated. The distributions of induced by twisting moments M33 and M11 birefringence at light propagation along X axis were obtained. it was established that birefringence don't induced by moment M33 at light propagation through geometrical centre of XY-cut of LiNbO3 crystals only (neutral point) and by moment M11 at light propagation in Y=0 plane only (neutral line). The results of experiment were explained on the base of optical indicatrix equations. The distributions of induced by bending deformation birefringence at light propagation along Z axis were obtained. It was established that birefringence don't induced at light propagation in Y=0 plane only (neutral line). The results of experiment were explained on the base of optical indicatrix equations. the accordance of induced by different ways bending to the idealised theoretical model was analysed. The gradient piezogyrational effect under the influence of twisting deformation was investigated in centrosymmetrical NaBi(MoO4)2 crystals. It was shown that twisting moment M33 induces the appearance of the turn of light polarisation plane r3 at light propagation along Z axis through geometrical centre of crystal cut, and twisting moment M11 induces the appearance of the turn of light polarisation plane r3 at light propagation in Y=0 plane. on the base of experimental results the components of gradient piezogyration tensor were estimated which are equal x3333=3.7ґ10-11 m/N and x3311=x3322=17.5ґ10-11 m/N.