TOPOLOGICAL CHARGE AND ANGULAR-MOMENTUM OF LIGHT-BEAMS CARRYING OPTICAL VORTICES

We analyze the properties of light beams carrying phase singularities, or optical vortices. The transformations of topological charge during free-space propagation of a light wave, which is a combination of a G aussian beam and a multiple charged optical vortex within a Gaussian e nvelope, are studied both in theory and experiment. We revise the exis ting knowledge about topological charge conservation, and demonstrate possible scenarios where additional vortices appear or annihilate duri ng free propagation of such a combined beam. Coaxial interference of o ptical vortices is also analyzed, and the general rule for angular-mom entum density distribution in a combined beam is established. We show that, in spite of any variation in the number of vortices in a combine d beam, the total angular momentum is constant during the propagation. [S1050-2947(97)09910-1].