【作者】 陈巧玲；

【导师】 周卫东；

【作者基本信息】 浙江师范大学 ， 光学， 2010， 硕士

【摘要】 激光诱导击穿光谱技术作为一种有效的物质成分分析技术,在很多领域都体现了应用潜力,如环境污染检测、工业工程监测、生物研究、安检、太空探索和艺术品古董检测等。而采用定标方法进行测量时,由于基体效应的影响容易造成测量误差,因此1999年A.CIUCCI提出了一种基于自由定标的激光诱导击穿光谱技术(CF-LIBS),这种方法不仅能够避免基体效应并且无需标准样品进行定标。到目前为止这种方法在很多领域都有相应的应用研究,但是由于这项技术的复杂性,还存在很多问题值得研究。CF-LIBS的主要优点是无需标准样品进行定标并且能够避免基体效应的影响,但对等离子体的探测条件要求比较高,需要选择合适的光谱采集窗口才能得到准确的测量结果。另外由于CF-LIBS是基于全谱的分析技术,所以对光谱的数据处理要求非常高。基于以上考虑,本文的主要研究内容包括：为了实现快速测量,编写了一个能够实现自动检峰、自动光谱干扰校正、自动元素归属确定和自由定标定量分析等功能的智能化分析程序,另外根据测量到的激光诱导等离子体的温度、电子密度的时间演化特性,研究了激光诱导等离子体的局部热平衡条件以及影响CF-LIBS测量结果的因素。第一章介绍了激光诱导击穿光谱技术的发展现状,激光诱导等离子体的基本概念和理论,包括等离子体的基本性质、诊断等离子体电子密度和电子温度的常用手段、等离子体发射光谱的加宽机制。第二章首先简要介绍了CF-LIBS的发展现状,然后详细的介绍了自由定标方法的原理和影响因素。第三章介绍了本文所用的LIBS实验装置,主要包括激光器,光谱测量系统。构建了自动、实用有效的LIBS光谱数据处理模型。通过协方差法和二阶求导法实现了光谱峰位的自动检测；针对谱线重叠干扰问题,采用谱线拟合法结合遗传算法对重叠干扰峰进行了有效的分解；最后对特征光谱所对应的元素标定原理与准则进行了归纳总结。第四章首先构建了等离子体电子密度和电子温度的计算模型,利用Stark展宽计算等离子体的电子密度,采用saha-boltzmann平面法获取等离子体的温度。通过时间分辨光谱研究了激光诱导等离子体的电子密度和电子温度的时间演化特性,在此基础上明确了等离子体局部热平衡条件,结果表明在500ns-1500ns的演化时间内土壤等离子体是满足局部热平衡条件的；构建了基于自由定标的定量分析系统,对国家标准物质(土壤GBW7429)中的Ca和Mg元素进行定量检测并探讨了在不同的延迟时间下的测量准确度,结果显示当延迟时间为500ns-1000ns时准确度最高,这与局部热平衡条件相符合；另外初步研究了光谱采集窗口和自吸收效应对测量结果的影响。最后,总结全文,并对进一步的研究工作提出了一些建议。更多还原

【Abstract】 Laser-Induced-Breakdown Spectroscopy (LIBS) is a recognized laser detection technique for sensing the chemical composition of a wide range of materials including environmental monitoring, industrial processing, Biomedical studies, military and safety needs, space exploration, and art works analysis. However the concentration of major components is difficult to measure by this method because of the so called "matrix effect". Fortunately, Calibration-Free laser-induced break down spectroscopy (CF-LIBS) which can correct the matrix effect was put forward by A.CIUCCI in 1999. It is a promising approach for quantitative analysis without using certified samples and calibration curves. So from then on, many researchers committed their efforts to this field and applied it to several other fields; however, much work is needed in the future study.CF-LIBS has advantages of eliminating the use of calibration curve and avoiding the matrix effect. It is a potential technique for analysis in many fields; however, it must find a suitbale observation winddow and a complex procedure is needed. So in this article, the main goal is to establish a spectrum data processing procedure which can intelligently fulfill the peek-seeking, overlapped spectral-correcting and qualitative analysis. Then study on the LTE condition and its effect on the accuracy of CF-LIBS.In chapter one, the basic concept, characteristic, diagnostic techniques, and the application of the laser-induced plasma are introduced briefly. Broadening of the spectral lines and two important characters of the emission spectral and the method to measure the electron temperature are presented.In the second chapter, a brief introduction of the CF-LIBS is presented. Then the theory of the CF-LIBS is introduced in detail. Finally it lists some factor that will affect the accuracy of CF-LIBS.In chapter three, the experimental setup and method are introduced in detail with the description of the ablation laser and spectrum detection system. An intelligent data preprocessing models was founded in this work. The automatic peak-seeking algorithm was based on the covariance and second derivative. For the resolution of overlapped spectral lines, a model based on the line-fitting and genetic algorithm was established and tested. The qualitative analysis rule was founded for automatic spectral line identification.In chapter four, the model for calculating the electron density and electron temperature of the plasma was founded. The electron density is gotten from the Stark-broadening of line at 422.67 nm, the electron density is gotten from the Saha-boltzmann plot. The temporal history of the plasma is obtained by recording the emission features at predetermined delays and at a fixed gate width (500ns). For each spectrum both electron density and excitation temperature are calculated for each delay time, the LTE condition is studied in shown that the LTE condition is validated when the delay time ranged from 1000ns to 1500ns. Then based on the principle of CF-LIBS, a procedure for elemental analysis is proposed. With help of the procedure, we studied the factors that affect the accuracy of the analysis results.Finally, the results of the whole research work are summarized and the directions for the further studies suggested.更多还原