Vortex algebra by multiply cascaded four-wave mixing of femtosecond optical beams

Experiments performed with different vortex pump beams show for the first time the algebra of the vortex topological charge cascade, that evolves in the process of nonlinear wave mixing of optical vortex beams in Kerr media due to competition of four-wave mixing with self-and cross-phase modulation. This leads to the coherent generation of complex singular beams within a spectral bandwidth larger than 200nm. Our experimental results are in good agreement with frequency-domain numerical calculations that describe the newly generated spectral satellites.This work was partially supported by the National Science Foundation (NSF)-Bulgaria and the Australian Research Council. P.H. acknowledges funding by the DFG