双脉冲飞秒激光诱导击穿光谱研究
发布时间：2018-12-24 12:39
【摘要】：激光诱导击穿光谱技术(Laser-induced breakdown spectroscopy,LIBS)是当今材料分析领域的一个研究热点。由于飞秒激光(femtosecond laser,fs laser)脉冲的超短持续时间,超高峰值功率,以及极低的热效应,采用飞秒激光作为光源来研究材料的诱导击穿光谱可以提高探测的空间分辨率,减少样品材料的去除量,实现超远距离探测等。然而相对纳秒激光,飞秒激光产生的等离子体的信号强度较弱,如何提高飞秒激光诱导击穿光谱(fs-LIBS)的信号强度是一个迫切需要解决的问题。采用共线双脉冲取代单脉冲可以有效提高飞秒激光诱导击穿光谱的信号强度。然而,双脉冲飞秒激光诱导击穿光谱的增强机理研究仍然充满争议或有待研究。基于这一背景,本文系统地研究了金属、半导体、有机电介质、以及火焰等不同物质的双脉冲飞秒激光诱导击穿光谱的信号随双脉冲延时的变化规律,通过飞秒激光与不同物质相互作用的机理深入探讨了双脉冲飞秒激光信号的增强机制。本论文研究工作的创新点概括如下:(1)通过研究金属材料铜的双脉冲fs-LIBS信号,发现导致信号增强的原因是第二个脉冲对第一个脉冲产生的等离子体羽辉的加热作用,使得等离子体进一步离化升温,寿命延长,从而使得探测光谱的信号增强。同时发现在较小的激光通量下的双脉冲fs-LIBS信号的增强倍数较高,且在1 ps内飞秒激光的脉冲宽度的变化对双脉冲fsLIBS没有影响。(2)通过对比半导体材料硅的双脉冲fs-LIBS信号与其烧蚀坑的表面形貌和烧蚀深度,揭示了造成硅的双脉冲fs-LIBS信号增强的主要原因是双脉冲飞秒激光的材料去除量大于单脉冲的材料去除量。(3)首次研究了有机电介质材料PMMA(聚甲基丙烯酸甲酯,俗称有机玻璃)的双脉冲fs-LIBS。发现其等离子体中的各粒子的信号增强倍数从大到小依次为离子、中性原子、分子。尽管其等离子体的动态变化过程受到周围空气影响,但是通过对电子密度和等离子体温度的研究发现造成其信号增强的主要机制与金属材料类似,也是第二个飞秒激光脉冲对第一个脉冲产生的等离子体羽辉的加热作用。(4)首次将双脉冲fs-LIBS用于火焰燃烧的研究。由于飞秒激光诱导产生的氧炔焰中CN信号与火焰的燃氧比成正比,说明fs-LIBS的CN光谱可以用来探测火焰的燃氧比。通过使用双脉冲fs-LIBS,CN光谱的信号强度得到了较大的增强,使得用双脉冲fs-LIBS探测火焰燃氧比的灵敏度提高。
[Abstract]:Laser induced breakdown spectroscopy (Laser-induced breakdown spectroscopy,LIBS) is a hot topic in the field of material analysis. Because of the ultrashort duration of femtosecond laser (femtosecond laser,fs laser) pulse, ultra-high peak power, and extremely low thermal effect, using femtosecond laser as a light source to study the induced breakdown spectrum of materials can improve the spatial resolution of the detection. To reduce the sample material removal amount, to achieve ultra-long-distance detection and so on. However, compared with nanosecond laser, the signal intensity of plasma produced by femtosecond laser is relatively weak. How to improve the signal intensity of femtosecond laser induced breakdown spectroscopy (fs-LIBS) is an urgent problem to be solved. The signal intensity of femtosecond laser induced breakdown spectrum can be improved by using collinear double pulse instead of single pulse. However, the enhancement mechanism of double pulse femtosecond laser induced breakdown spectroscopy is still controversial. Based on this background, the variation of the double pulse femtosecond laser induced breakdown spectra of metals, semiconductors, organic dielectrics, flame and other materials with double pulse delay is systematically studied in this paper. The enhancement mechanism of double pulse femtosecond laser signal is discussed through the interaction mechanism between femtosecond laser and different matter. The innovations of this thesis are summarized as follows: (1) by studying the double pulse fs-LIBS signal of copper, it is found that the cause of the signal enhancement is the heating effect of the second pulse on the plasma plume produced by the first pulse. The plasma is further ionized and the lifetime is prolonged, which enhances the signal of the detection spectrum. At the same time, it is found that the enhancement times of dual-pulse fs-LIBS signal are higher at low laser flux. The pulse width of femtosecond laser has no effect on the double pulse fsLIBS within 1 ps. (2) by comparing the double pulse fs-LIBS signal of the semiconductor silicon with the surface morphology and ablation depth of the ablation pit, It is revealed that the main reason for the enhancement of double pulse fs-LIBS signal of silicon is that the material removal of double pulse femtosecond laser is larger than that of single pulse. (3) the organic dielectric material PMMA (polymethyl methacrylate) is studied for the first time. Double pulse fs-LIBS. (commonly known as plexiglass) It is found that the signal enhancement times of each particle in the plasma are ion, neutral atom and molecule in order from large to small. Although the dynamic process of the plasma is influenced by the ambient air, it is found that the main mechanism of the signal enhancement is similar to that of the metal material through the study of the electron density and the temperature of the plasma. It is also the second femtosecond laser pulse to heat the plasma plume produced by the first pulse. (4) the double pulse fs-LIBS is used for flame combustion for the first time. Because the CN signal produced by femtosecond laser induced oxyacetylene flame is proportional to the ratio of combustion to oxygen, the CN spectrum of fs-LIBS can be used to detect the ratio of combustion to oxygen. The signal intensity of double pulse fs-LIBS,CN spectrum is greatly enhanced, which makes the sensitivity of detecting flame fuel to oxygen ratio improved by using double pulse fs-LIBS.
【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB302.5
[Abstract]:Laser induced breakdown spectroscopy (Laser-induced breakdown spectroscopy,LIBS) is a hot topic in the field of material analysis. Because of the ultrashort duration of femtosecond laser (femtosecond laser,fs laser) pulse, ultra-high peak power, and extremely low thermal effect, using femtosecond laser as a light source to study the induced breakdown spectrum of materials can improve the spatial resolution of the detection. To reduce the sample material removal amount, to achieve ultra-long-distance detection and so on. However, compared with nanosecond laser, the signal intensity of plasma produced by femtosecond laser is relatively weak. How to improve the signal intensity of femtosecond laser induced breakdown spectroscopy (fs-LIBS) is an urgent problem to be solved. The signal intensity of femtosecond laser induced breakdown spectrum can be improved by using collinear double pulse instead of single pulse. However, the enhancement mechanism of double pulse femtosecond laser induced breakdown spectroscopy is still controversial. Based on this background, the variation of the double pulse femtosecond laser induced breakdown spectra of metals, semiconductors, organic dielectrics, flame and other materials with double pulse delay is systematically studied in this paper. The enhancement mechanism of double pulse femtosecond laser signal is discussed through the interaction mechanism between femtosecond laser and different matter. The innovations of this thesis are summarized as follows: (1) by studying the double pulse fs-LIBS signal of copper, it is found that the cause of the signal enhancement is the heating effect of the second pulse on the plasma plume produced by the first pulse. The plasma is further ionized and the lifetime is prolonged, which enhances the signal of the detection spectrum. At the same time, it is found that the enhancement times of dual-pulse fs-LIBS signal are higher at low laser flux. The pulse width of femtosecond laser has no effect on the double pulse fsLIBS within 1 ps. (2) by comparing the double pulse fs-LIBS signal of the semiconductor silicon with the surface morphology and ablation depth of the ablation pit, It is revealed that the main reason for the enhancement of double pulse fs-LIBS signal of silicon is that the material removal of double pulse femtosecond laser is larger than that of single pulse. (3) the organic dielectric material PMMA (polymethyl methacrylate) is studied for the first time. Double pulse fs-LIBS. (commonly known as plexiglass) It is found that the signal enhancement times of each particle in the plasma are ion, neutral atom and molecule in order from large to small. Although the dynamic process of the plasma is influenced by the ambient air, it is found that the main mechanism of the signal enhancement is similar to that of the metal material through the study of the electron density and the temperature of the plasma. It is also the second femtosecond laser pulse to heat the plasma plume produced by the first pulse. (4) the double pulse fs-LIBS is used for flame combustion for the first time. Because the CN signal produced by femtosecond laser induced oxyacetylene flame is proportional to the ratio of combustion to oxygen, the CN spectrum of fs-LIBS can be used to detect the ratio of combustion to oxygen. The signal intensity of double pulse fs-LIBS,CN spectrum is greatly enhanced, which makes the sensitivity of detecting flame fuel to oxygen ratio improved by using double pulse fs-LIBS.
【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB302.5
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