Spectrum superbroadening in self-focusing of pulsed vortex beams in air

Based on numerical simulations, self-focusing of conventional and vortex optical beams produced by femtosecond pulses in air is comparatively analysed. It is shown that, other things being equal, in the case of self-focusing of vortex beams, a significantly higher concentration of energy is observed in the focal spot. As a consequence, there also arises a significant broadening of the space – time spectrum of the focused vortex beam as compared with the vortex-free self-focusing regime. The azimuthal instability of the vortex structure at small initial perturbations of the wave front leads to filamentation of radiation at distances greater than is usually the length of self-focusing.