Vortices in ultrashort laser pulses
Peter Hansinger, Alexander
Dreischuh, and Gerhard G. Paulus
Abstract.
The propagation of optical vortices nested in broadband femtosecond
laser beams was studied both numerically and experimentally. Based on the
nonlinear Schrödinger equation, the dynamics of different multiple vortex configurations
with varying topological charge were modeled in self-focusing and self-defocusing
Kerr media. We find a similar behavior in both cases regarding the vortex–vortex
interaction. However, the collapsing background beam alters the propagation for
a positive nonlinearity. Regimes of regular and possibly stable multiple filamentation were identified this way. Experiments include
measurements on pairs of filaments generated in a vortex beam on an astigmatic
Gaussian background with argon gas as the nonlinear medium. Spectral broadening
of these filaments leads to a supercontinuum which
spans from the visible range into the infrared. Recompression yields <19
fs pulses. Further optimization may lead to much
better recompression.