Abstract

Recent work has shown that lasers and photorefractive oscillators (PROs) can emit fields with vortices which circle about the optical access [I]. These patterns are the consequence of simultaneous emission of helical fields with high topological charge phase singularities together with rotationally symmetric fields such as the fundamental Gaussian mode. We report experiments on the transient dynamics that occur when the cavity of a photorefractive oscillator (PRO) is tuned between patterns containing different numbers and charges of vortices. Specifically, a pattern with four circling vortices undergoes a metamorphosis into a pattern with five oppositely circling vortices of the same topological charge with one additional oppositely charged vortex in the center. The total topological charge of both patterns is the same whereas the total number of vortices differs by two so that a "vortex pair" has been created during the transition between the patterns. The observed patterns are quantitatively simulated using an empirically chosen superposition of passive cavity helical modes.

© 1996 Optical Society of America