Reconstruction of stable states of spiral vortex beams

Using an asymptotic approach and an experiment supported by computer simulation, we analyzed processes of restoring structural stability and transitions to new stable states of spiral vortex beams subject to perturbations by curly apertures. Using a tetragonal beam as an example, we considered three perturbation scenarios: 1) asymmetric perturbation, when an opaque screen covers the caustic only on one side of the square, 2) symmetric perturbation, when the curly aperture covers the entire beam except for a narrow caustic region, and 3) symmetric perturbation, when the curly aperture screens only a narrow region of the caustic without affecting the rest of the beam. At the same time, the asymptotic calculation was carried out for all types of polygonal beams. It was shown that if the curly aperture did not destroy the caustic region of the spiral beam, it was able to self-heal in the far diffraction zone. If the perturbation even locally destroyed a part of the caustics, then the perturbed beam passed into a new stable state through chains of creation and annihilation of optical vortices (dislocation reactions).