Filamentation of Femtosecond Vortex Beam in Sapphire

Abstract

Filamentation of powerful femtosecond beams with a vortex of the topological charge l = 2 in sapphire is studied. A method to control the azimuthal position of filaments by changing the phase difference between two coherent co-axial beams, vortex and vortex-free reference ones, is proposed and demonstrated. The observed misalignment between the paths of filaments generated by the vortex and vortex-free beams, when they cross at a small angle is explained in terms of the spiral propagation of filaments around the vortex optical axis.