Vortex solitons in an off-resonant Raman medium
  We investigate existence and linear stability of coupled vortex solitons supported by cascaded four-wave mixing in a Raman active medium excited away from the resonance. We present a detailed analysis for the two- and three-component vortex solitons and demonstrate the formation of stable and unstable vortex solitons, and associated spatio-temporal helical beams, under the conditions of the simultaneous frequency and vortex comb generation. 
A. V. Gorbach, D. V. Skryabin, and C. N. Harvey