Rotational characteristics of an array of optical vortices in a self-defocusing medium

We report experimental investigations of the nonlinear propagation of an array of optical vortices with the same topological unity charges through a self-defocusing Kerr medium. The rotation angle was strongly dependent on the vortex density and was not uniform for each vortex pair. Numerical results were in good agreement with experimental results. We explained such behavior by considering the vortex-vortex interaction which is distinctive when the dark core profiles of optical vortices are localized in space.