EXCITATION OF VORTEX SOLITONS IN A GAUSSIAN-BEAM CONFIGURATION

An investigation of dark spatial solitons in the form of optical vorti ces in a resonant nonlinear medium is reported for the first time. A b eam from a CW laser with a singly charged vortex nested on its axis wa s passed through a cell with rubidium atomic vapour at low concentrati ons. A substantial squeezing of the vortex core and spreading of the b eam profile is observed when the nonlinearity increases. The soliton b ehaviour is analysed numerically and is found to be strongly affected by the saturation of nonlinearity, by the absorption, and by the prope rties of the Gaussian background beam. A new method of controlling the spatial position of a vortex soliton is discussed.