Strong-Field-Induced N$_{2}^{+}$ Air Lasing in Nitrogen Glow Discharge Plasma
Nana Dong1†, Yan Zhou1†, Shanbiao Pang1, Xiaodong Huang1, Ke Liu1, Lunhua Deng1*, and Huailiang Xu1,2,3,4*
1State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China 2State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China 3Chongqing Institute of East China Normal University, Chongqing 401120, China 4CAS Center for Excellence in Ultra-intense Laser Science, Shanghai 201800, China
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 $B^{2}\!\varSigma_{\rm u}^{+}(v'=0)$–$X^{2}\!\varSigma_{\rm g}^{+} (v'' =0)$ 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 $B^{2}\!\varSigma_{\rm u}^{+}(v'=0)$ 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 $B^{2}\!\varSigma_{\rm u}^{+}$ and $X^{2}\!\varSigma_{\rm g}^{+}$ states of N$_{2}^{+}$, in which a much higher population occurs in the $X^{2}\!\varSigma_{\rm g}^{+}$ 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 $X^{2}\!\varSigma_{\rm g}^{+}$ state in the discharged medium.
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2021, Vol. 38 
