L. Stoyanov, G. Maleshkov,
In this work we show both experimentally and by numerical simulations that the presence and evolution of ring dark beam and/or on-axis optical vortex nested on a bright background beam noticeably perturb the host background. In a photorefractive nonlinear medium (crystal SBN) these perturbations can initiate self-focusing of the background. By changing the dark ring radius and the presence of an optical vortex and keeping all other experimental parameters unchanged, we can control the dynamics at the initial stage of longitudinal self-focusing and the type of self-focusing structure (single peak or bright ring of variable radius). The presented results may appear especially important in experiments that involve cascaded nonlinear frequency mixing of singular beams, in which accelerated dark beam spreading is accompanied by self-focusing of certain portions of the perturbed host beam.
Keywords: Nonlinear optics, transverse effects in; Photorefractive optics; Self-action effects; Optical vortices