Spiral-like singular beams in gyrotropic crystals

Recent developments in solving a paraxial wave equation¹ open new perspectives in theoretical analysis of different types of singular beams stimulating in turn a great series of experimental investigations ^2,3. In particular, authors of Ref.⁴ propose to use pure phase masks for creating a structurally stable helico-conical singular beam with spiral-like intensity distribution. On the other hand, artificial phase masks need a great precision in their manufacturing connected with a large industrial outlay. Because of a great interest is to use natural objects for generating singularities in beams. Such objects are anisotropic crystals. As is well-known, uniaxial and biaxial crystals serve as basic elements for generating optical vortices nested in different types of singular beams ⁵. The most amazing feature of the crystal is ability to create stable polychromatic vortices with high energy effectiveness. In contrast to the method of computer-generated holograms^6,7 the crystal forms a white vortex-bearing beam without any additional gadgets. The aim of the present article is to consider one more way permitting to generate singular beams bearing spiral edge dislocations and optical vortices with the help of two gyrotropic crystals.