超光学衍射限高空间分辨的双波长激光剥离-激光诱导击穿光谱元素显微分析

To realize super-diffraction-limited high spatial resolution microscopic analysis of the localized elements in solid samples, a dual-wavelength laser-ablation (LA) laser-induced breakdown spectroscopy (LIBS) technique will be studied based on one nanosecond Nd:YAG laser and with two wavelength combinations (These are 532-1064nm and 266-1064nm combinations.) The tasks of this project include: (1) to realize time delay of the 1064nm laser pulse by quartz fiber with large core diameter; (2) to determine laser-ablation thresholds accurately for different samples with LIBS; (3) to enhance spectroscopic detection sensitivity with time-resolved photon-counting technique; (4) to achieve super-diffraction-limited high spatial resolution under ideal focusing and near-threshold laser-ablation conditions; and (5) to realize high spatial resolution elements microscopic analysis to biological samples and alloys. The dual-wavelength LA-LIBS technique will be systematically established after thorough studies in this project. A super-diffraction-limited high spatial resolution microscopic analysis of both major and minor elements in samples can be realized, and the spatial resolution can be reached to 200 nm and even less than 200 nm. This project can not only solve the problem of the contradiction between high spatial resolution and high detection sensitivity existed in single pulse LIBS with good scientific meaning, but also its technical results can be broadly applied in biology, medical science, material science, microelectronics and nano science, etc.

为了实现固体样品中微区元素的超光学衍射限高空间分辨显微分析,本项目拟开展基于一台纳秒Nd:YAG激光器的532-1064nm和266-1064nm两种波长组合的双波长激光剥离(LA)-激光诱导击穿光谱(LIBS)研究。采用大芯径石英光纤实现1064nm激光的延时；用LIBS准确测定不同样品的激光剥离阈值；采用时间分辨单光子计数技术提高光谱检测灵敏度；在理想的聚焦条件和近阈值的剥离条件下,获得超光学衍射限的高空间分辨本领；并利用所建立的技术开展生物样品和合金的高空间分辨元素显微分析。该项目可以系统地建立起双波长LA-LIBS技术,实现对样品中主要元素和微量元素的高空间分辨显微分析,空间分辨本领达到200nm甚至更高的水平。该项目不仅可以较好地解决LIBS研究中高空间分辨本领和高灵敏度之间的矛盾,具有较大的科学意义；其技术成果还可以在生物、医学、材料科学、微电子和纳米科学等领域获得广泛的应用。

为了从根本上解决传统的单脉冲激光诱导击穿光谱技术在对样品元素进行显微分析时所存在的高空间分辨本领和高光谱分析灵敏度之间的矛盾，本项目提出并研究了正交双脉冲双波长激光剥离—激光诱导击穿光谱技术（ODPDWLA-LIBS，简称DWLA-LIBS），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，将样品剥离与击穿这两个物理过程分开并分别予以优化，以实现高空间分辨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单元技术进行了研究。包括用大芯径石英玻璃光纤传输高能脉冲激光、固体样品激光剥离阈值和激光焦点光斑尺寸的精确测量、门控光电倍增管和门控前置信号放大器的研制以及将光子计数器用于原子辐射信号检测等。. 然后基于单台纳秒脉冲Nd:YAG激光器搭建了DWLA-LIBS实验系统，开展了532-1064 nm和266-1064 nm两种波长组合的DWLA-LIBS技术在合金元素显微分析上的应用基础研究，并建立了相关的定量分析方法；还对应地开展了基于皮秒激光的DWLA-LIBS研究工作。. 对于纳秒脉冲激光，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可以达到亚微米水平。样品表面最小可观测烧蚀坑洞直径为880 nm，空间分辨本领小于500 nm，突破了光学衍射限的限制。. 项目研究共发表了8篇SCI收录的论文，4篇EI收录的论文；申请4项专利；参加7次学术会议交流以及培养了9名硕士研究生。. DWLA-LIBS可以弥补扫描电镜技术在分析绝缘样品和轻元素时的不足，可以获得比x射线荧光技术更高的光谱分析灵敏度和更高的空间分辨本领。它可以广泛用于材料科学、生命科学、采矿、文物鉴定等众多领域的二维或者三维的元素显微分析，具有重要的科学意义和良好的应用前景。