基于远程空气激射的新型大气监测拉曼技术研究

With today’s growing concern for the environment, traditional Raman technique, due to its low signal-to-noise ratio with limited temporal resolution and detection range, has faced increasing challenges in remote atmospheric real-time monitoring. Femtosecond laser filamentation, with unique ability of kilometer range nonlinear propagation persistent under adverse conditions, provides an attractive potential tool for atmospheric remote sensing. In particular, the recent observation of remote air lasing during femtosecond laser filamentation allows the generation of in situ, coherent laser source for remote Raman excitation, indicating a longer-range Raman technique for atmospheric monitoring. More importantly, due to the pre-excitation of molecules to vibrational/rotational states impulsively by the femtosecond laser pulse, the efficiency of Raman scattering by air lasing will be distinctly improved. Based on the above-mentioned research background, this project aims to carry out detailed investigations on such remote Raman scattering induced by air lasing. Several key issues, such as signal-to-noise ratio, long-range propagation and detection, and the generation of backward signal, will be focused on in this project to develop a new atmospheric diagnostic technique with high sensitivity.

随着人类对环境问题的日益关注，传统的拉曼测量技术由于信噪比不高，在大气监测上存在着许多限制，如时间分辨率有限，探测高度有限，难以满足对大气环境远距离实时监测的需求。飞秒激光成丝，由于具有独特的远程传输能力并且不受恶劣天气环境影响等优点，在大气远程监控方面具有重要的应用价值。特别是最近飞秒激光成丝相干空气激射现象的发现，为远程拉曼散射提供了原位、相干激光光源，有望进一步提高大气拉曼测量的探测高度。更重要的是，由于飞秒激光脉冲对气体分子振动、转动态的冲击预激发，空气激射所产生的拉曼散射信号具有高信噪比的优点。基于以上研究背景，本项目拟对空气激射诱导的远程拉曼散射进行细致研究，重点解决信噪比、远程传输与探测、背向传输信号获取等关键科学问题，发展具有高灵敏度的大气诊断新技术。

飞秒激光成丝，由于具有独特的远程传输能力并且不受恶劣天气环境影响等优点，在大气远程监控方面具有重要的应用价值。特别是最近飞秒激光成丝相干空气激射现象的发现，为远程拉曼散射提供了原位、相干激光光源，有望进一步提高大气拉曼测量的探测高度。在本项目研究中，我们针对氮气离子产生远程空气激射、中性氮气分子产生的背向空气激射，在产生机制和偏振依赖开展了深入研究，为进一步揭示空气激射的物理起因，和空气激射诱导拉曼散射的进一步优化提供了依据。本项目研究中产生的探测分子激发态新方法，弥补了分子动力学探测的不足，对于原子分子的研究，也起到了借鉴和推进的意义。