Generation of white-light optical vortices through four-wave mixing
Optical vortices (OVs) are singular optical beams with a spiral phase dislocation in their wavefront. When two pump beams at the frequencies ω 1 and ω 2 interact in a Kerr-type nonlinear medium, the degenerate four-wave mixing (FWM) process results in the generation of new distinct sum and difference frequency components at the output. Importantly, the FWM process is expected to preserve the topological charge of the OVs, and thus it can be employed for the generation of white-light vortices, in contrast to the vortex propagation in a Raman nonlinear medium [1]. However, as the FWM process is accompanied by noticeable nonlinear instabilities due to self- and cross-phase modulation, the phase information in the newly generated frequency components may be destroyed [2]. Therefore, it is important to reveal the possible regimes where the FWM process will dominate nonlinear instabilities, leading to the stable generation of white-light optical vortices.