基于共心多径腔增强的高灵敏双脉冲LIBS微量元素分析原理与技术研究

Laser-induced breakdown spectroscopy (LIBS) can be applied to coal chemical industry (coal to olefins, coal to oil, etc.) with advantages of simultaneous and rapid multi-element analysis. However, the detection limits of some elements are difficult to meet the practical application requirements. This project is aimed to develop a multipass cell coupled orthogonal double-pulse LIBS (DP-LIBS) technology based on concentric multipass cavity enhancement to fully interact plasma plume with laser energy, so as to significantly improve the LIBS detection sensitivity and reduce the detection limits. The temporal and spatial distribution of multi-ionized particles in the initial and re-excited plasma will be studied by using the differential monochromatic imaging and the spatial-resolved image reconstruction. The temporal and spatial distribution of the temperature, electron density, and ionization degree before and after the second excitation will be studied by using the plane matrix spectra scanning and the plasma spectra chromatography. Based on the temporal and spatial distribution characteristics of multi-ionized particles and plasma parameters, we can analyze the interaction between laser, plasma and particles, and finally form the double-pulse LIBS concentric multipass cavity enhancement theory for both pre-ablation and reheating modes. The method and technology of this project not only open up a new way for the realization of microelement analysis LIBS system with high sensitivity, low detection limit, and high spatial and temporal resolution, but also provide a theoretical support for the spectra enhancement mechanism of plasma.

激光诱导击穿光谱（LIBS）用于煤化工（煤制烯烃、煤制油等）分析具有多元素同时快速分析的优势，但部分元素的检测限难以满足行业分析要求。本项目拟发展基于共心多径腔增强的多通池耦合正交双脉冲DP-LIBS微量元素分析技术，使激光能量充分作用于等离子羽，大幅提高LIBS分析灵敏度并降低检测限；同时，利用差分单色成像和空间分辨图像重构，研究初始和再激发等离子体中多电离态粒子的时空分布；利用平面矩阵光谱扫描和等离子体光谱层析，研究二次激发前后等离子体温度、电子密度和电离度的时空分布；基于多态粒子和等离子体特征参数的时空分布特性，分析激光与等离子体及粒子间的相互作用，形成预烧蚀与再加热的双脉冲LIBS共心多径腔增强机制理论。本项目方法和技术不仅为高灵敏、低检测限、高时空分辨的LIBS微量元素分析系统的实现开辟新的途径，而且为等离子体的光谱增强机制提供理论支撑。

项目研究组基于热传导、轴对称流体动力学及局部热平衡态辐射方程进行理论分析，建立了正交双脉冲LIBS 共心多径腔增强等离子体膨胀的二维辐射流体动力学模型，仿真了等离子体数密度、膨胀速度、电子温度的时空演化，并利用辐射传输方程得到等离子体增强发射光谱的分布，从等离子体-等离子体耦合效应和压力效应两个方面获得了谱线强度的增强机制；发展了基于光谱、空间和时间分辨双波长差分成像的时空分辨光谱层析技术，并用其研究了激光诱导等离子体中多电离态粒子的时空分布结构的演化机制与激光支持波传播机制间关系；发展了高灵敏的共心多径腔增强预烧蚀DP-LIBS分析技术，充分利用腔内共心多径反射路径稳定、反射周期稳定的优势，使激光能量充分激发等离子羽，促进等离子体内上能级粒子数密度增加、温度均衡，使得光谱信号较正交再加热DP-LIBS增强了3.6倍，对微量元素的检测灵敏度满足了行业应用要求。利用以上理论和技术成果，通过时间分辨率光谱采集和控制，采用高灵敏的正交双脉冲LIBS 共心多径腔增强检测技术，利用多能态粒子数反演、主成分降维、小波变换及支持向量机，建立了激光诱导光谱至燃煤灰分、挥发分及发热量指标的转化模型，对燃煤工业指标中高位发热量、灰分、挥发分分析的均方根误差分别达到0.85MJ/kg、1.82%和1.22%，对煤中As、Mn、Cu的检测限分别达到了76.3ppm、6.8ppm和18.6ppm。项目实施期间，项目组共发表论文16篇，其中SCI论文14篇，授权国家发明专利2项、在受理国家发明专利3项，毕业博士3人、硕士1人。总体完成了项目考核任务要求，达到了预期目标。