飞秒激光成丝在燃烧场中诱导的相干激射及其在远程燃烧诊断中的应用研究

The traditional combustion diagnosis methods based on laser spectrum have limited signal-to-noise ratio, resolution and detection distance, especially the fluorescence signals detected are strongly influenced by the quenching effect, which is a common phenomenon and dramatically reduces the fluorescence intensity in the high-temperature and high-pressure combustion environment. Femtosecond laser filamentation, with unique ability of kilometer range nonlinear propagation persistent under adverse conditions, provides an attractive potential tool for remote combustion diagnosis. In particular, it has recently been discovered that the CN coherent lasing-like emissions generated by femtosecond laser filaments in the combustion field have the advantages of high coherence, high sensitivity, narrow bandwidth, small emission angle and long distance transmission, etc. At the same time, there are many complex ultra-fast physical processes in the process of flame coherent lasing-like emissions, which provides a new method to study the super-fast dynamics of intense-field molecular physics and chemical combustion. Based on the above research background, this project intends to combine ultra-fast nonlinear spectrum technology with remote combustion diagnosis to study the coherent lasing-like emissions induced by femtosecond laser filaments in combustion field in detail, and focus on clarifying the mechanism of the coherent lasing-like emissions, exploring the dynamic process of ultra-fast combustion in strong field, simulating the remote transmission and detection of combustion products.

传统的基于激光光谱的燃烧诊断方法，其信噪比、分辨率、探测距离有限，特别是在高温高压燃烧环境下会发生荧光淬灭，难以满足实际燃烧诊断的需求。飞秒激光成丝具有独特的远程传输能力并且不受恶劣环境影响，在远程燃烧诊断方面具有重要的应用价值。特别是最近发现了飞秒激光成丝在燃烧场中产生的CN自由基相干激射，由于其具有高相干、高灵敏度、窄带宽、发射角小、远距离传输等优点，为实现高灵敏度远程火灾探测和燃烧诊断提供新思路新方法。与此同时火焰相干激射产生过程内含许多复杂超快物理过程，为研究强场分子物理和化学燃烧超快动力学提供了一种全新手段。基于以上研究背景，本项目拟将超快非线性光谱技术与远程燃烧诊断相结合，对飞秒激光成丝在燃烧场诱导的远程相干激射进行细致研究，重点澄清火焰相干激射的产生机制、探索强场中的超快燃烧动力学过程、模拟远程传输与燃烧产物探测，为其在复杂燃烧环境诊断、火灾探测等领域的应用奠定基础。

传统的基于激光光谱的燃烧诊断方法，其信噪比、分辨率、探测距离有限，特别是在高温高压燃烧环境下会发生荧光淬灭，难以满足实际燃烧诊断的需求。飞秒激光成丝具有独特的远程传输能力并且不受恶劣环境影响，在远程燃烧诊断方面具有重要的应用价值。飞秒激光成丝在燃烧场中诱导的自由基相干激射，由于其具有高相干、高灵敏度、窄带宽、发射角小、远距离传输等优点，为实现高灵敏度远程火灾探测和燃烧诊断提供新思路新方法。与此同时火焰相干激射产生过程内含许多复杂超快物理过程，为研究强场分子物理和化学燃烧超快动力学提供了一种全新手段。基于以上研究背景，本项目采用1030nm超短激光脉冲作为泵浦，诱导燃烧自由基C2、CH和CN的多波长荧光信号，系统研究了以上荧光信号对激光中心波长、泵浦能量、泵浦光偏振状态、聚焦条件、燃烧场与光丝作用空间位置等实验条件的依赖，发现了燃烧产物的荧光发射可以通过控制飞秒激光的特性来有效地实现，实现了对燃烧自由基非线性光谱的相干调控，这一发现有助于优化燃烧自由基分子荧光的信噪比，为飞秒激光在燃烧动力学及燃烧产物探测等领域的进一步应用奠定了基础；通过开展飞秒激光在乙醇火焰和空气中诱导三次谐波产生（THG）的对比实验，发现了燃烧场中飞秒激光成丝诱导的THG放大现象，分析了THG放大倍率对焦距、火焰和光丝的相对位置等实验参数的依赖，并通过实验提出了观察到的THG的增强是源自于高温加热下气体密度受到干扰进而对Gouy相移产生了抑制作用，基于TH信号放大倍率对燃烧场温度的敏感性，研发了基于飞秒激光成丝的燃烧场温度远程非接触测量方法，对飞秒激光成丝诱导的非线性光谱技术在复杂燃烧诊断、火灾探测等领域中的应用奠定了基础。