Quasimonochromatic optical vortices

The propagation of a circularly polarized singular beam through a single-axis crystal is accompanied by the appearance of additional singularities in the polarization structure of the beam field. These vector singularities combine to form concentric umbilic lines-degenerate umbilic point of the star type, thus significantly changing the entire structure of the field. When the beam passes though a birefringent quarter-wave plate and a polarizer, the vector singularities transform into the usual optical vortices. Rotation of the polarizer and/or of the quarter-wave plate drives the vortices to move by preset trajectories, merge with one another, or break into elementary singularities