The Angular Distribution of Optical Emission Spectroscopy from a Femtosecond Laser Filament in Air

Spatial characterization of a femtosecond laser pulse filament in air is experimentally investigated by detecting the optical emission spectroscopy of laser-induced plasmas. It is shown that the intensity of N I spectral lines have different angular distributions along the filament and the calculated results fit the experimental data well. The obtained degree of atomic polarization along the filament strongly depends on the electron density and the propagation characteristic of the femtosecond laser pulse.