Abstract

Large-scale computer simulations of wide-beam, high-power femtosecond laser pulse propagation in air will be presented. Our model is built around the nonlinear Schrodinger equation and incorporates the main effects present in air including diffraction, group-velocity dispersion, absorption and defocusing due to plasma, multiphoton absorption, nonlinear self-focusing and rotational stimulated Raman scattering The vectroial field equation is coupled to a Drude model that describes the plasma density evolution. We are interested in intense femtosecond pulses with powers significantly exceeding the critical power for self-focusing in air. During propagation, multiple light filaments form and feed on the energy from a low-intensity background[1]. High intensities in collapsing filaments generate plasma, which in turn causes strong defocusing and thereby regularizes the collapse events. A large part of the energy localized in a collapse is returned to the background reservoir and can be used for formation of other filaments: we term this process dynamic spatial replenishment[2].

© 2000 IEEE