【作者】 许洪光；

【导师】 崔执凤；

【作者基本信息】 安徽师范大学 ， 原子与分子物理， 2007， 硕士

【摘要】 对聚焦激光辐照固体表面形成激光等离子体的研究,在实际生产和生活中的诸多领域得到广泛应用,例如在超导薄膜、纳米材料研制、同位素分离、医学、生物学、环境科学及其他应用领域有着重要的理论研究价值和广泛的应用前景。而激光诱导击穿光谱(Laser-induced Breakdown Spectroscopy,简称LIBS)技术正是利用激光等离子体的发射光谱来定量分析样品中各种元素的成份。LIBS技术所具有的潜在高灵敏度、无须对样品进行繁杂的预处理、对分析样品具有极小的破坏性以及可用于远程测量等特点,已引起人们的广泛关注,并已在合金中的微量元素定量分析、锅炉中微量元素含量的控制等诸多领域得到成功应用,但将LIBS技术应用于土壤中微量重金属元素定量分析的研究工作报道不多。本文从实验上测定土壤样品在可见光波段(300-450nm)的LIBS谱,对实验测定的光谱进行了分析和归属,得到了土壤中微量重金属元素Pb的LIBS检测限,并探讨了采用自由定标处理方法定量分析土壤样品中元素含量的可行性。第一章介绍了等离子体的基本概念,主要包括激光等离子体的基本性质和特性、常用的激光等离子体诊断手段以及激光等离子体发射光谱的应用。第二章简述了有关激光等离子体的基本理论,主要包括激光等离子体的空间结构、激光等离子体的简化模型、激光等离子体中发射光谱线的加宽、以及激光等离子体电子温度的测定方法。第三章介绍了实验装置,主要包括激光光源、光谱测量系统以及样品的配置流程。第四章主要从实验上研究了土壤中微量重金属元素Pb的激光诱导击穿光谱,具体内容包括:(1)从实验上测定土壤在可见光谱区的LIBS光谱,对测定的光谱结构进行了分析,并对可观测的谱线进行了归属,得出土壤所含的主要元素和部分微量元素。实验结果表明,土壤中的主要元素是Si、Al、Fe、Mg等,Mn、Pb、Cr等是土壤中的微量元素;(2)测定了不同Pb搀杂浓度下土壤中微量重金属元素Pb 405.78nm谱线的强度,采用内标法拟合得到该分析谱线的LIBS定标曲线,由定标曲线的拟合结果计算得到该实验条件下土壤样品所含铅元素的检测限。第五章主要介绍采用自由定标方法(CF-LIBS)对土壤中的主要含量元素进行定量分析,包括两个部分内容:(1)通过对实验获得的土壤样品的LIBS谱进行分析,得到该实验条件下激光诱导等离子体的电子温度Te,其范围为4200-4500K;(2)在此基础上,利用自由定标的处理方法对土壤样品中Si、Al、Fe、Mg等十种主要元素进行了定量分析,并给出这十种主要含量元素在土壤样品中的含量。更多还原

【Abstract】 The investigation on the laser induced micro-plasma by the radiation focused on a solid surface plays an important role in the production of super-conduct films and nanometer materials, laser isotope separations, medicine, biology, and other industrial applications. Elemental analysis based on the emission from the plasma generated by focusing a high power density laser beam on a solid sample surface is known as laser-induced breakdown spectroscopy (LIBS). LIBS has power potential to be used to detect trace elements in the sample matrix that include gases, aerosols, and liquids. The high sensitivity of the technique, the free sample preparation, the minimal destroy of the sample, and its suitability to remote measurements are generally concerned by scientific researchers. LIBS has successfully used to detect the trace elements in metal alloy and the control of the trace element concentration in stove, but there are few works reported on the application of LIBS to quantitative detection of the heavy metal elements in soil. The focus of this thesis is listed as following: The experimental measurement, analysis, and assignment of the LIBS spectra of the soil in the visible spectral region(300-450nm) are studied. The LIBS detection limit for Pb element in soil is also obtained. The application of the calibration-free method in the quantitative elements analysis is discussed finally.In chapter one, the basic concept, characteristic, some diagnostic techniques, and the application of the laser-induced plasma are introduced briefly.In the second chapter, a brief introduction of the basic theory about the laser plasma, the space structure of the laser plasma, several models to deal the laser induced plasma dynamics, the broadening of the spectral lines and two important character of the emission spectral, and the method to measure the electron temperature are presented.In chapter three, the experimental setup and method are introduced in detail with the description of the ablation laser, spectrum detection system and preparation of the soil samples.In chapter four, we investigate on the Laser-induced breakdown spectroscopy of the trace metal element Pb in Soil. The main contents are as followings: (1) The LIBS spectra of the soil are measured in the visible spectral region in our experiment. The main and some trace elements of the soil sample are obtained by the analysis and the assignment of spectral structure and spectra lines respectively. The experimental results show that the major elements in soil sample are Si, Al, Fe, Mg and so on and the trace elements are Mn, Pb, Cr. (2) Additionally, the intensities of Pb 405.78nm spectral line are measured at the different concentration of Pb in soil. The LIBS calibration curve of the analytical spectra line is obtained by internal calibration, and the value of detection limit, 36.7ppm, is obtained from the fit of the calibration curve.In the last chapter, the Calibration-Free method is applied in the quantitative major elemental analysis in soils, the main contents are as followings: (1) The elements contained in the soil sample are presented by the analysis of the measured laser-induced breakdown spectroscopy in our experiment and the plasma electron temperature,4200-4500K,is obtained from the measured spectral line intensities of the Laser-induced breakdown spectroscopy. (2) Based on the results mentioned above, we make an investigation on the concentration of the ten major elements such as Si、Fe、Al、Mg etc. in soil by calibration-free method and their content in soil are obtained as well.更多还原