Strong-Field-InducedN2+AirLasinginNitrogenGlowDischargePlasma

We investigate N2+ air lasing at 391 nm,induced by strong laser fields in a nitrogen glow discharge plasma.We generate forward N2+ air lasing on the B2Σu+（v'=0）-X2Σg+（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 B2Σu+（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 N2+ lasing is caused by the efficient suppression of population inversion between the B2Σu+ and X2Σg+ states of N2+,in which a much higher population occurs in the X2Σg+ state in the discharge plasma.Our results clarify the important role of population inversion in generating N2+ air lasing,and also indicate the potential for the enhancement of N2+ lasing via further manipulation of the population in the X2Σg+ state in the discharged medium.