Re-Heating Effect on the Enhancement of Plasma Emission Generated from Fe Under Femtosecond Double-Pulse Laser Irradiation

In this paper, we present a study on the effect of inter-pulse delay using femtosecond double-pulse laser-induced breakdown spectroscopy in a collinear geometry. The temporal evolution of spectral intensity is performed for the lines of Fe I 423.60 nm, Fe I 425.08 nm and Fe I 427.18 nm. It is found that, by selecting appropriate inter-pulse delay, the signal enhancement can be significantly increased compared with the single-pulse case. A three-fold enhancement in the current experiment is obtained. The plasma temperature and electron density are also investigated based on the theory of Boltzmann plot and Stark broadening. We attribute the main mechanism for emission enhancement to the plasma re-heating effect.     

激光诱导击穿光谱分析钛合金铸件三维成分分布

TiAl类金属间化合物Ti-47.5Al-2.5V-1.0Cr为有潜力的轻量化高温合金,用于精密铸造高温部件。成分配比和铸造工艺影响该钛合金铸件质量和使用性能,有必要研究其三维(3D)空间成分分布。实验利用激光诱导击穿光谱(LIBS)在设定的多个位置进行深度激发,获得每个位置激发深度对应的测量数据。将对应位移系统3D坐标的全部测量数据组合成矩阵,将三维位移系统的3D坐标转换为样品实际测绘的3D坐标,抽取一定比例的多层分布面数据、经Matlab模拟得到3D-成分分布全貌,建立了成分的3D空间分布方法。对Ti-47.5Al-2.5V-1.0Cr涡流器进行3D近表面分析,获得了不同以往的成分分布形态认知。C、Ca元素的层状正偏析平行于样品表面,Cr、V元素的层状负偏析斜交于表面。剔除40 μm表层后计算得到的该钛合金的Al、Ti原子比中位值为1.02,接近配料比值1.03。     

利用脉冲激光预诱导激发产生增强等离子体及其性质的研究

利用普通电焊枪对金属样品进行烧蚀时,由于温度限制,产生的激发等离子体无法满足局部热平衡条件,导致测量等离子体性质出现许多受限条件,如连续多帧光谱全噪声采样信号、基底效应影响和电子温度波动较大等。为解决此问题,提出利用一束短脉冲NdYAG激光器结合精密数字延时脉冲发生器的方法,让该短脉冲激光束平行于样品表面照射进行预激发,再通过电焊枪垂直于样品表面进行二次电离产生高温等离子体。实验结果表明,这种利用短脉冲激光预激发的方式所产生的等离子体特征光谱信号强度大幅增强和电子温度得到提高,最高可达45倍,同时连续采集时特征光谱全噪声信号帧数明显降低,信噪比也得到很好的提高。另外,还讨论了短脉冲激光预激发时间和光纤探测端面几何位置对测量结果的影响。     

Laser‐induced breakdown spectroscopy for photovoltaic silicon wafer analysis

The principal subject matter of this work is the application of laser‐induced breakdown spectroscopy for the multi‐elemental analytical characterization of different qualities of solid silicon. The physical process upon which the technique is based is the temporally resolved observation of emission spectra emitted by a micro‐plasma generated by a laser focused on the surface of a given sample. The optimal environmental parameters such as the composition of the buffering gas for the identification and measurement of several metallic, non‐metallic, and dopant impurities were determined. Particular attention was given to boron. A detection limit of 2.10⁻⁴ mg/g of boron was found using a calibration curve, which was made in the range of 1 to 100 ppmw. Silicon samples from different production techniques (4C and directional solidification), which permit the segregation of different impurities along the length of the silicon ingot were analyzed using laser‐induced breakdown spectroscopy. Copyright © 2011 John Wiley & Sons, Ltd.     

激光诱导击穿光谱技术研究的新进展

激光诱导击穿光谱技术（LIBS）是一种基于原子发射光谱学的物质组分分析技术。随着激光技术和光学检测技术的发展,激光诱导击穿光谱技术已经成为光谱学领域的研究热点。尤其是近几年,LIBS技术发展迅速,涌现出多种LIBS的激发和探测新技术。在光谱激发方面,出现了如飞秒激光及飞秒激光大气中长距离成丝诱导击穿光谱技术,双脉冲激光诱导击穿光谱技术等。在光谱探测方面,出现了时间分辨激光诱导击穿光谱技术,偏振分辨激光诱导击穿光谱技术等。本文将对这几种LIBS中所出现的新技术进行介绍并给出LIBS技术的发展趋势。     

激光诱导击穿光谱在金属材料在线分析方面的应用进展

激光诱导击穿光谱(LIBS)由于具有无需样品制备、分析速度快、可远距离在线遥测以及可进行元素的二维表面分布和深度分析等特点,引起光谱化学分析领域研究者的广泛关注。在冶金过程工艺控制领域,金属材料的在线分析以及元素多维信息的获取,对于实时监控金属材料的生产工艺及准确实现金属材料的快速分类方面具有重要的意义。与传统的分析方法相比较,LIBS技术因其众多优势已成为金属材料实时在线分析的最佳手段之一,而且已有多种商品化的仪器推出。论文首先对LIBS在线仪器装置进行介绍,然后对近些年LIBS在熔融金属在线分析、连铸钢坯鉴别、炉渣在线分析、金属材料分类识别、金属材料镀层分析等方面的发展现状及挑战进行论述,最后对LIBS在线分析进行展望。     

Electric-field induced fluctuations in laser generated plasma plume

The effect of an external electric field on laser-generated plasma has been studied. It is observed that the laser-generated plasma can be used for the ignition of a spark in the presence of a low voltage external electric field. An eight-fold emission intensity enhancement in Cu Ⅰ spectral lines are measured as compared to the signal intensity in the absence of an external electric field.The plasma parameters remain the same initially, up to a few microseconds after the generation of plasma, and this feature makes it more interesting for the quantitative analysis of any sample using laser induced breakdown spectroscopy(LIBS). In the presence of an external electric field,fluctuations(contraction and expansion) in the laser-generated plasma are observed which increase the plasma decay time and consequently result in enhanced signal intensity.     

一种两阶段变量选择的LIBS定量分析方法

使用机器学习方法结合激光诱导击穿光谱(Laser Induced Breakdown Spectroscopy,LIBS)进行定量分析,变量选择的结果直接影响最终的定标模型.现有的变量选择方法多存在需要先验知识、计算量庞大等问题,因此提出一种两阶段变量选择方法.第一阶段为排序阶段,以皮尔逊相关系数r为排序准则快速排除与...     

基于激光诱导击穿光谱积分信号的水稻种子鉴别研究

基于LIBS技术结合BP神经网络技术,对6类水稻种子进行类型鉴别研究.对水稻种子的LIBS全谱和分段光谱进行积分,再输入BP神经网络,得到:全谱积分前的识别率为81.02％,积分后识别率为93.40％,识别率提高12.38％;分段光谱积分后识别效果较好的是中心波长为405 nm、570 nm、810 nm的光谱,将这三...