Reconfigurable beam shaping in parametric wave mixing

Abstract

Summary form only given. Singular light beams, that contain topological wave front dislocations, are ubiquitous entities that display fascinating properties with widespread important applications. Screw dislocations, or vortices, are a common dislocation type. They are spiral phase-ramps around a singularity where the phase of the wave is undefined and its amplitude vanishes. Vortices appear spontaneously in several settings, including in speckle-fields, in optical cavities and in the doughnut laser modes, and otherwise they can be generated with phase masks, or with astigmatic optical-components. The order of the screw dislocation multiplied by its sign is referred to as the topological charge of the dislocation. Vortices also form by self-wave front modulation in nonlinear optical media. In this context, parametric mixing of multiple waves containing wave front dislocations in quadratic nonlinear media constitutes a fascinating scenario We report investigations of the dynamics of evolution of screw phase-dislocations existing in the wave front of a Gaussian beam with nested multiple-charged vortices that propagate in quadratic nonlinear crystals under conditions for seeded second-harmonic generation. The number of existing vortices, and their location, is shown to depend on the input light and material conditions, including the topological charge, width and intensity of the pump and seed signals, as well as on the propagation length inside the crystal. Spontaneous vortex pair nucleation consistent with the above predictions was observed in our experiments in KTP cut for Type II phase-matching at /spl lambda/=1.064 /spl mu/m.