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arXiv · 2504.18124

Influence of molecular rotation on the generation of N$_2^+$ air lasing

Wenli Yang·Ping Li·Luzhen Yang·Jianfeng Guo·Pengji Ding·Shan Xue·Hongchuan Du
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Abstract

N$_2^+$ air lasing has attracted considerable attention due to its promising applications in remote sensing and the debates surrounding its generation mechanisms. Here, we present a comprehensive theoretical investigation of the role of molecular rotation in N$_2^+$ lasing at 391 nm ($B^2 \Sigma _u^+(v''=0)\rightarrow X^2 \Sigma _g^+ (v=0)$). By solving the open-system density matrix and Maxwell-Bloch equations in a rovibronic-state basis, we examine both the formation of the N$_2^+$ gain medium induced by a femtosecond pump pulse and the subsequent spatial propagation of the seed pulse. During the pump stage, rotational dynamics are found to significantly modify the angle-dependent populations of ionic vibrational-electronic states within tens of femtoseconds. Furthermore, ionization-produced rotational coherences substantially enhance the population inversion between the $X^2 \Sigma _g^+ (v=0)$ and $B^2 \Sigma _u^+(v''=0)$ states. In the seed propagation stage, both population inversion and rotational coherence are found to contribute to the lasing process, with the latter playing a dominant role in amplifying the lasing signals. These findings reveal the crucial role of molecular rotation in N$_2^+$ air lasing and highlight its potential as a tunable parameter for controlling lasing dynamics.

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Wenli Yang, Ping Li, Luzhen Yang, Jianfeng Guo, Pengji Ding, Shan Xue, Hongchuan Du. 2025-04-25. Influence of molecular rotation on the generation of N$_2^+$ air lasing. https://arxiv.org/abs/2504.18124

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