Generation and expansion of laser-induced plasma as a spectroscopic emission source

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy （LIBS） has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermo-dynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.

激光烧蚀光谱-电感耦合等离子体质谱联用技术在地质分析中的应用

激光烧蚀光谱(LAS)技术具有空间分辨率高,样品用量少,制样简单,分析速度快,可远程、实时、在线分析多相物质(气态、液态、固态)的特点,是近年来发展迅速的一种分析技术,具有广阔的应用前景,但它对痕量元素的分析能力不足。电感耦合等离子体质谱(ICP-MS)技术具有灵敏度高和多元素及同位素同时检测的能力,在微痕量元素精密分析方面具有很大的优势,但对基体元素分析存在困难。将LAS和ICP-MS技术相结合,形成LAS和LA-ICP-MS联用技术(LAS-ICP-MS),可充分利用两种技术的优势,形成互补技术,为地质分析提供一种便捷、可靠的分析手段:利用LAS技术,可预先监测样品的大致含量与信号的稳定性等参数,筛选适用于LA-ICP-MS分析的样品,避免因元素含量过高引起的LA-ICP-MS采样锥锥口易堵塞,基体效应过大,以及因样品均匀性差或激光参数未优化等因素影响分析的准确性和精密度等问题;利用LA-ICP-MS技术,可对激光进样条件和原子化、离子化条件分开进行优化,从而改善仪器的分析性能。将LAS-ICP-MS用于岩石矿物分析,表现出其良好的应用前景。

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Nd：YAG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。