Strong-Field-Induced N2+ Air Lasing in Nitrogen Glow Discharge Plasma

Abstract

We investigate N 2 + air lasing at 391 nm, induced by strong laser fields in a nitrogen glow discharge plasma. We generate forward N 2 + air lasing on the B 2 Σ u + ( v ′ = 0 ) – X 2 Σ g + ( v ″ = 0 ) transition at 391 nm by irradiating an intense 35-fs, 800-nm laser in a pure nitrogen gas, finding that the 391-nm lasing quenches when the nitrogen gas is electrically discharged. In contrast, the 391-nm fluorescence measured from the side of the laser beam is strongly enhanced, demonstrating that this discharge promotes the population in the B 2 Σ u + ( v ′ = 0 ) state. By comparing the lasing and fluorescence spectra of the nitrogen gas obtained in the discharged and laser-induced plasma, we show that the quenching of N 2 + lasing is caused by the efficient suppression of population inversion between the B 2 Σ u + and X 2 Σ g + states of N 2 + , in which a much higher population occurs in the X 2 Σ g + state in the discharge plasma. Our results clarify the important role of population inversion in generating N 2 + air lasing, and also indicate the potential for the enhancement of N 2 + lasing via further manipulation of the population in the X 2 Σ g + state in the discharged medium.