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

A femtosecond light filament which is a long range propagating coherent structure resulting from the saturation of self-focusing by a single mechanism is shown. This process leads to asymmetric pulse temporal profiles and spectra, while other propagation regimes lead to symmetric modulated pulses and are therefore not compatible with femtosecond filamentation. Thus, an estimation of the electron density is obtained from the oscillation period for the pulse intensity. Such results lead to a new interpretation of femtosecond filamentation in air.