Dynamics of femtosecond filamentation from saturation of self-focusing laser pulses

An interpretation is proposed for the dynamics of light filaments formed when a femtosecond laser pulse propagates in air. The pulse evolves as a set of coupled nonlinear oscillators forming a coherent structure over several Rayleigh lengths. The plasma generated by photoionization is numerically shown to be the single saturation mechanism of the beam self-focusing. Other physical processes such as group velocity dispersion and the quintic susceptibility chi((5)) for the polarization promote different propagation regimes. From theoretical expressions of the oscillation period for the spatial profile of the pulse, we show that the electron density in a femtosecond filament may be estimated.