Zheng Wei, Miao Zhiming, Dai Chen, Wang Yang, Liu Yi, Gong Qihuang, Wu Chengyin
State Key Laboratory for Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China.
Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China.
J Phys Chem Lett. 2020 Sep 17;11(18):7702-7708. doi: 10.1021/acs.jpclett.0c02337. Epub 2020 Sep 1.
Backward amplified spontaneous emission of neutral nitrogen molecules has been reported from laser-induced plasma filaments. The cavity-free UV emission has great potential applications in remote atmospheric sensing. However, the formation mechanism for the excited nitrogen molecules inside filaments remains controversial. Here we study the formation mechanism of excited nitrogen molecules pumped by intense femtosecond laser pulses. After modification of the electron energy distribution by inclusion of the recollision between the electron and its parent ion as well as modification of the electron collision cross section by inclusion of the secondary electron contribution, the theoretical calculations reproduce the experimental observations very well. The results clearly demonstrate that excited nitrogen molecules are generated through collisions between energetic electrons and neutral nitrogen molecules.
据报道，在激光诱导的等离子体细丝中存在中性氮分子的反向放大自发辐射。这种无腔紫外发射在远程大气传感方面具有巨大的潜在应用价值。然而，细丝内部激发态氮分子的形成机制仍存在争议。在此，我们研究了由强飞秒激光脉冲泵浦产生的激发态氮分子的形成机制。通过考虑电子与其母离子之间的重碰撞来修正电子能量分布，并通过考虑二次电子贡献来修正电子碰撞截面后，理论计算结果与实验观测结果非常吻合。结果清楚地表明，激发态氮分子是通过高能电子与中性氮分子之间的碰撞产生的。
