摘要
激光诱导击穿光谱技术(LIBS)作为一种新兴的化学分析手段,因其具备实时、可多元素同时探测、原位等优势,在工业化在线检测领域具有巨大潜力。设计一套基于伽利略式望远镜的气体LIBS探测系统,采用5组不同透镜组合作为聚焦光路,对比分析聚焦距离200 mm下氮氧混合气体的LIBS定性定量结果,其中1组为焦距200 mm的单透镜,其他4组为凹透镜(f=-50.8 mm)和不同双凸透镜组合组成的伽利略式望远系统,双凸透镜组合采用4个凸透镜(f分别为75、100、125、150 mm)分别与同一凸透镜(f=200 mm)组合的形式。结果表明:相比于单透镜,双凸透镜组合的击穿阈值较低,选用焦距为125 mm和200 mm的双凸透镜组合能够获得最高的LIBS谱线强度和最好的信号稳定性,通过Zemax光学模拟发现,该透镜组合具有适中的焦深和聚焦角度,有利于获得更高质量的LIBS信号;在定量分析中,计算相对标准偏差(RSD)、均方根误差(RMSE)和检出限(LOD),发现双凸透镜组合的使用能够明显改善定标曲线相关系数,提高预测稳健性和探测灵敏度,相较于单透镜,双凸透镜组合下LIBS预测信号的稳定性提高1.5倍以上,RMSE降低至0.678以下,检测能力提升9.9倍以上。双凸透镜组合的使用能够在工业气体在线检测中发挥重要作用。
Objective High-purity nitrogen and oxygen are essential as protective gases for many high-precision instruments,directly affecting their performance and detection sensitivity.It is crucial to develop methods suitable for industrial production processes,which have significant implications for scientific research and industrial applications.Laser-induced breakdown spectroscopy(LIBS),an emerging chemical analytical method,holds the potential for quantitative analysis in industrial detection due to its real-time,in-situ,and multi-element detection capabilities.However,due to field application constraints, standoff detection using LIBS has become ineffective for measuring industrial gases. The detection sensitivityof the system significantly decreases with increasing detection distance, leading to difficulties in obtaining effective plasmasignals and performing quantitative analysis. Therefore, more effective excitation methods are needed. Recent studies onLIBS quantitative analysis have predominantly focused on liquid and solid phases, while plasma generation in air and itsradiation characteristics are notably different. Effective plasma emission depends largely on an optimal focusingarrangement. We evaluate the breakdown threshold and signal stability for different focusing arrangements, analyzing thedifferences in line intensities among five focusing arrangements. Two typical focusing arrangements are analyzed to detailtheir quantitative performance for various gas mixtures, advancing the practical application of LIBS in measuring industrialgases.Methods A Nd∶YAG all-solid-state laser operating in Q-switched pulse mode at a fundamental wavelength of 1064 nmwith a repetition rate of 20 Hz is used as the excitation source. The pulse width is 8 ns, and the laser beam diameter isapproximately 6 mm. A portion of the laser energy is reflected through a beam splitter to an energy detector for real-timemonitoring. The laser is focused on the gas sample using various focusing arrangements. The gas mixture, consisting ofhigh-purity liquid oxygen and liquid nitrogen, is prepared using a custom-built mass flow controller. Spectral measurementsare conducted with plasma emission collected by a system with a focal length of 50.8 mm and coupled into a delivery fiber.The spectrometer has a wavelength range of 200‒900 nm and a spectral resolution of 0.3 nm. The laser operates in internaltrigger mode, with the spectrometer synchronized to the laser pump signal. Five focusing arrangements—CDC_(1), CDC_(2),CDC_(3), CDC_(4), and SL1—are analyzed. Four arrangements use Galilean telescope systems comprising a combination ofconcave lenses (f=-50.8 mm) and biconvex lenses, while SL1 uses a single lens (f=200 mm) for comparison.Results and Discussions Time-resolved emission spectra under nitrogen-oxygen gas mixture conditions are obtained(Fig. 2). The line intensity decreases with increasing delay. Given the lower background radiation at the early plasma stagefor N and O atomic lines, an optimal detection delay of 100 ns is chosen. Typical spectra and peak areas for O Ⅰ 777.4 nmfor the five arrangements at 100 ns are illustrated (Fig. 3). Differences in line intensity among the five arrangements areattributed to the spot radius of the focusing lens and the depth of focus. Signal stability for different arrangements iscalculated from 200 replicate spectra (Fig. 4). The biconvex lens arrangement significantly improves signal stabilitycompared to that of the single lens arrangement (SL1). Further analysis of spectral differences, considering the depth offocus and optical simulation (Figs. 5 and 6), reveals that CDC_(3) achieves the highest line intensity due to its moderatefocusing angle and shorter depth of focus, while SL1 has the longest depth of focus and root mean square (RMS) radius,resulting in the lowest line intensity. The simulation and calculation results for other arrangements are consistent withFig. 3. To evaluate LIBS quantitative performance, CDC_(3), and SL1 are used to measure oxygen-in-nitrogen and nitrogenin-oxygen gas mixtures at various concentrations (Figs. 7 and 8). The biconvex lens arrangement provides higher spectralline intensity and signal stability, enhancing detection sensitivity.Conclusions In this study, we investigate the influence of different focusing arrangements on the qualitative andquantitative performance of LIBS. Five focusing arrangements—CDC_(1), CDC_(2), CDC_(3), CDC_(4), SL1—are examined.Combining emission spectra acquisition with Zemax simulation, we explore line intensity differences among thearrangements. Results show that the biconvex lens arrangement offers a lower breakdown threshold than the single lens.The highest LIBS spectral line intensity and signal stability are achieved with the biconvex lens combination (CDC_(3)) withfocal lengths of 125 and 200 mm, due to its moderate depth of focus and focusing angle, as confirmed by Zemaxsimulation. In quantitative analysis, the combination of biconvex lenses can improve the correlation coefficient ofcalibration curves, while also enhancing prediction robustness and detection sensitivity. The stability for CDC_(3) is increasedby over 1.5 times compared to SL1, and the root mean square error (RMSE) is reduced to less than 0.678, with thedetection ability increased by more than 9.9 times. The CDC focusing arrangements can significantly enhance real-timeindustrial gas detection.
作者
张嘉旭
陈晨
李楠
骆益凡
赵阳阳
管今哥
郑永秋
薛晨阳
Zhang Jiaxu;Chen Chen;Li Nan;Luo Yifan;Zhao Yangyang;Guan Jinge;Zheng Yongqiu;Xue Chenyang(School of Instrument and Electronics,North University of China,Taiyuan 030051,Shanxi,China;State Key Laboratory of Dynamic Measurement Technology,North University of China,Taiyuan 030051,Shanxi,China;Xi’an Aerospace Propulsion Institute,Xi’an 710025,Shaanxi,China;National Key Laboratory of Solid Rocket Propulsion,Xi’an 710025,Shaanxi,China)
出处
《光学学报》
CSCD
北大核心
2024年第22期238-247,共10页
Acta Optica Sinica
基金
国家自然科学基金(62305314)
山西省基础研究计划(202203021222066)
山西省回国留学人员科研资助项目(2023-132)。
关键词
激光诱导击穿光谱
氮氧混合气体
透镜组合对比
光谱辐射特性
定性定量分析
laser-induced breakdown spectroscopy
oxygen-nitrogen gas mixture
comparison of lens combination
spectral radiation characteristic
qualitative and quantitative analysis
