Study of the population inversion mechanisms and superradiance on ion transitions of molecular nitrogen in the filament

The experimental results of the inversion population mechanisms study in the resonant electronic transition B3g–A3Su+of nitrogen ions by optically pumped of air and pure nitrogen by femtosecond laser pulse at a wavelength of 950 nm arepresented. It is shown that the inversion results from selective settling of N2+(B2Su+, v' =0) excited state by multiphotonexcitation of the autoionization states of the nitrogen molecule with energy of 18.7 eV. Seed photon for superradiance attransitions of molecular nitrogen ions are photons the axial supercontinuum occurring in the filament on the respectivewavelengths. The mode of the superradiance at a wavelength l = 358.4 nm referred to the transition of the CN moleculeswas realized