正交双波长双脉冲LA-LIBS技术及其在原位元素显微分析中的应用

To solve the problem of the contradiction between spatial resolution and analysis sensitivity exists in single pulse laser-induced breakdown spectroscopy, the orthogonal dual-wavelength dual-pulse laser-ablation laser-induced breakdown spectroscopy (LA-LIBS) technique is proposed in this project. Where 532nm or 266nm laser pulse is focused by high quality objective with large numerical aperture to improve spatial resolution, and 1064nm laser pulse is used to excite the ablated sample from the direction which is perpendicular to the propagation direction of ablation laser beam to enhance analysis sensitivity. Thus in-situ microscopic analysis of elements with both high spatial resolution and high sensitivity can be realized. The tasks of this project include: (1) to transfer 1064nm laser pulse by quartz fiber with large core diameter and to realize time delay of less than 250ns. (2) to determine ablation threshold of the ablated samples with LA-LIBS accurately. (3) to achieve submicron spatial resolution under ideal focusing and near-threshold laser-ablation conditions;(4) to realize in-situ high spatial resolution elements microscopic analysis for some solid samples, such as alloys contain high priced metals. The limits of detection of common metal elements can be reached to 50ppm. This technique is helpful for overcoming the shortcomings of SEM and LA-ICP-MS/AES, and can be valuably used in different fields, such as material science, life science, microelectronics, historical relic identification, etc.

为了从根本上解决激光诱导击穿光谱技术中空间分辨本领与灵敏度之间的矛盾，本项目提出了正交双波长双脉冲LA-LIBS的研究思想。用高质量大数值孔径显微物镜聚焦532nm或者266nm激光来剥离待分析样品，提高空间分辨本领；同时采用1064nm的近红外激光从垂直方向来二次激发被剥离的样品以提高光谱分析的灵敏度，实现对样品的高空间分辨高灵敏的原位元素显微分析。研究采用大芯径石英玻璃光纤传输1064nm激光脉冲并实现250ns以内的延时；精确测定样品的剥离阈值；在理想的聚焦和近阈值的剥离条件下，获得亚微米尺度的空间分辨本领。并利用所建立的技术开展贵金属合金等固体样品元素的原位显微分析，常见金属元素的检出限达到50ppm的水平。其技术成果可以弥补扫描电镜和激光剥离-电感耦合等离子体-质谱/原子发射光谱等分析技术的不足，在材料科学、生命科学、微电子、文物鉴定等领域具有较大的应用价值。

为了解决激光诱导击穿光谱技术中空间分辨本领与灵敏度之间的矛盾，本项目提出并研究了正交双波长双脉冲激光剥离-激光诱导击穿光谱（LA-LIBS）技术。该技术通过正交传输的不同波长的两个激光脉冲先后作用于样品，将样品的剥离和击穿这两个物理过程进行适当的分离并分别予以优化，以实现高空间分辨本领和高光谱分析灵敏度的元素显微分析。. 项目首先对其中的关键技术进行了研究。包括采用大芯径石英玻璃光纤传输1064nm激光脉冲并实现250ns以内的延时；精确测定样品的剥离阈值；门控光电倍增管和门控前置信号放大器的研制等。其次，基于单台Nd:YAG激光器搭建了正交双波长LA-LIBS研究系统，开展了532-1064 nm和266-1064 nm两种波长组合的LA-LIBS技术在合金等固体样品元素上的原位显微分析。采用266-1064 nm波长组合，在烧蚀坑洞直径为6.5微米的条件下银饰品中铜元素的检出限可达到37.4 ppm；532-1064 nm波长组合下分析铝合金中的主量铝元素时，空间分辨本领小于500 nm，超出了光学衍射限的限制。. 项目研究共发表3篇SCI收录的论文，3篇EI收录的论文；申请2项专利；参加3次学术会议交流；培养了5名硕士研究生。. 正交双波长双脉冲LA-LIBS技术的成果可以弥补扫描电镜和激光剥离-电感耦合等离子体-质谱/原子发射光谱等分析技术的不足，在材料科学、生命科学、微电子、文物鉴定等领域具有较大的应用价值。.