On the method for measuring piezooptic coefficients pi(25) and pi(14) in the crystals belonging to point symmetry groups 3 and `3

Abstract

In the present work we describe a high-accuracy torsion method for measuring piezooptic coefficients π 14 and π 25 in trigonal crystals. Spatial distributions of the optical indicatrix orientation and the optical birefringence induced by torsion stresses are quantitatively evaluated and analysed. It is shown that a crystal subjected to torsion stresses works as an optical lens, with the characteristics operated by a torque moment.

Measurements of piezooptic coefficients pi(14) and pi(25) in Pb5Ge3O11 crystals using torsion induced optical vortex

“…Recently we have suggested a new high-accuracy torsion method for studies of piezooptic effect in solids [1][2][3][4][5]. As shown in our works, the method generally provides fairly high accuracy for piezooptic coefficients.…”

“…If the crystals under analysis are twisted, the distribution of the shear stress components 4 σ and 5 σ around Z axis may be written as [15] 4 4…”

“…Let us notice that, in the case of cubic crystals, one can determine a combination of the coefficients π 11 , π 12 , π 13 and π 44 under torsion torque applied around {111} direction (see [7]). For the crystals of 3 and 3 symmetry groups, the coefficients π 14 and π 25 are measurable when the torsion is applied around the optic axis and the light propagates along the same direction [5]. The experimental geometries needed for crystals of the other symmetries remain more complicated.…”

“…the groups 3m, 3m , 3, 3 , 32, 432, m3, 23, and 43m [3,5,7]. Let us notice that, in the case of cubic crystals, one can determine a combination of the coefficients π 11 , π 12 , π 13 and π 44 under torsion torque applied around {111} direction (see [7]).…”

“…Nonetheless, it is known [5,7,11] that the torsion of crystals belonging to the both trigonal and cubic symmetry groups is accompanied by appearance of an optical vortex, whenever the crystal sample is placed between circular polarisers. Then the intensity distribution in a wide cross section of a nearly plane-wave optical beam transmitted through the output circular polariser is very peculiar: the intensity remains equal to zero in the beam centre and a bright ring is observed around a central dark region.…”