Vortex avalanche in the perturbed singular beams.

Abstract

We have theoretically and experimentally considered transforming a single optical vortex beam into the vortex avalanche caused by weak local perturbations of the holographic grating responsible for the beam shaping. The vortex avalanche is accompanied by a sharp change of the orbital angular momentum (OAM) so that its dependence on the holographic grating perturbations forms the OAM spectrum. We revealed that the restored vortex beam has anomalous regions of the OAM spectrum in a form of sharp dips and bursts (resonances) that occur when the integer perturbation parameter coincides with a topological charge of one of the vortex modes. We found also that the intensity of the perturbed beam is nonuniformly distributed among the vortex modes with positive and negative topological charges. They form two groups of satellites with clearly marked intensity maxima. As the grating perturbation increases, the initial beam intensity is almost completely pumped over into the vortex avalanche with nearly the same energy redistribution among the satellites.