We show the dynamics of the evolution of screw phase dislocations in the wave fronts of Gaussian beams with nested multiple-charged vortices that propagate in quadratic nonlinear crystals under conditions for seeded second-harmonic generation. The number of existing vortices is shown to depend on the input light and material conditions, including the topological charge, the width and intensity of the pump and seed signals, and the propagation length inside the crystal. A closed-form model, which holds for arbitrary topological charges of the pump and seed inputs under conditions of negligible depletion of the pump beam, is developed to predict the number of vortices that exist at any instant in the propagation. It is discovered that different combinations of input charges yield a fascinating variety of vortex patterns. © 2000 Optical Society of America

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