Torsion-induced optical "triaxiality" of LiNbO3 crystals

In the present work we have revealed that three topological defects of optical indicatrix orientation appear whenever torsion stresses are applied to LiNbO3 and a divergent optical beam is incident upon this crystal. The above defects have half-integer strengths. We have found that the places where the defects are localized are characterized by a zero phase difference. These phenomena enable one to consider the three defects as outlets of optic axes in an inhomogeneous, 'optically triaxial' LiNbO3 crystal. After analyzing all of possible scenarios for the interaction among the defects, we have shown that no reaction of their fusion can be expected. Besides, there can appear no defects with intermediate strength values ranging from 1/2 to 1 and, moreover, no optical vortices with fractional charge are generated by these defects.