Polarization singularities of optical fields caused by structural dislocations in crystals

Abstract

We analyze polarization singularities of optical beams that propagate through crystals possessing structural dislocations. We show that screw dislocations of crystalline structure can lead to the appearance of purely screw-type dislocations of light wavefronts. This can happen only in crystals that belong to trigonal and cubic systems. These polarization singularities will give rise to optical vortices with the topological charge equal to ±1, whenever a crystal sample is placed between crossed circular polarizers. We have also found that edge dislocations present in the cubic and trigonal crystals, with the Burgers vector perpendicular to the three-fold symmetry axes, can impose mixed screw-edge dislocations in the wavefronts of optical beams and generate singly charged optical vortices. The results of our analysis can be applied for detecting and identifying dislocations of different types available in crystals.

Topological defects of optical anisotropy parameters caused by the screw dislocations of crystalline structure

“…(3) have earlier been used in Refs. [13,14]. Here the stress tensor components tend to infinity when the X and Y coordinates are equal to zero.…”

“…As shown in Ref. [13], the transverse spatial distribution of piezooptically induced optical birefringence in the particular case of screw dislocations gives birth to the distribution of polarization states in the beam cross section, which is characterized with a so-called singular C-point.…”

“…This allows for operating the efficiency of spin-to-orbit angular momentum conversion [9][10][11][12]. Recently we have shown that dislocations of a crystalline structure can also produce the wave front dislocations [13,14]. The latter property can be used while detecting and studying the imperfections of a real crystalline structure.…”

“…The latter property can be used while detecting and studying the imperfections of a real crystalline structure. In particular, we have found that screw dislocations in crystals produce the topological defects (TD) of optical indicatrix (OI) orientation that have their strength equal to ½ [13,14], while the edge dislocations produce the TD of OI orientation with the strength equal to unity [14].…”

Topological defects caused by inhomogeneity of optical activity

“…Moreover, the TDs can be produced by conically distributed electric fields, due to electrooptic Pockels and Kerr effect [15,16]. They can also arise due to piezooptic effect caused by the mechanical strains appearing around structural dislocations in solid crystals [17]. It would be natural to assume that the TDs of optical indicatrix orientation similar to those induced by the electrooptic Kerr effect can be generated using magnetic fields, due to a known Cotton-Mouton effect, since the structures of the relevant constitutive tensors are the same.…”