Femtosecond pulses in air: linear and nonlinear regime

In linear regime the single and few cycle femtosecond (fs) pulses propagates on several diffraction lengths changing their shape in semi-spherical (or parabolic) form, far away from plane wave and paraxial approximation. The experiments with fs pulses in air with power little above the critical for self-focusing (nonlinear regime) demonstrated new nonlinear effects as self-guiding, THz longitudinal emission and superbroad enlarging of the spectrum. In this paper we continue with developing of new theoretical model for quantitative description of the above experimental results.