The fine structure of singular beams in crystals: colours and polarization

The conversion of singular beams in a uniaxial crystal and their fine structure were experimentally studied. It is shown that the given system is able to generate singular beams in a wide spectral range. The fine structure of the 'white' singular beam has three levels: the polarization structure, the structure of the topological charge and the structure of the colours. It is revealed that the 'white' vortex can be defined by means of three experimentally measurable values: the orbital parameter SL (or the 3 ellipticity of the vortex core Q), the probability to meet such a vortex state W and the noise of the vortex core P (or the polarization degree in the given space point). The mathematical formalism for describing the vortex parameter on the complex plane and its stereographic projection is worked out. The independent characteristic of the 'white' optical vortex is also its colour gamut near the phase singularity. The degenerate and perturbed 'white' vortices are created. It is shown that the vector singularity in the 'white' beam does not have colouring, the vector singularity having gained colouring only after passing through the polarization filter.