【作者】 郭连波；

【导师】 曾晓雁； 陆永枫；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2012， 博士

【摘要】 激光诱导击穿光谱(Laser-induced breakdown spectroscopy,简称为LIBS)是采用聚焦的高能量脉冲激光入射到样品的表面产生等离子体,通过分析该等离子体的辐射光谱,从而推导出样品的元素组成成分及含量。LIBS技术具有很多显著优点：能够探测所有元素,可同时检测多种元素,无需真空,样品制备简单或无需制备,被分析样品几乎无损,可以实时分析,原位探测和远程探测等。因此自出现以来,LIBS技术就引起大家的广泛注意,并成为极有实用价值的光谱分析技术之一。目前该技术已成功应用于高危险的化学和生物分析、地质勘探、艺术品的检测以及深空探测等众多领域。但是,探测极限差、分析精度低,导致LIBS的探测灵敏度低已成为该技术发展的瓶颈问题,如何进一步提高探测灵敏度也是未来LIBS技术的主要研究方向。本论文的主要研究工作分别采用新型的空间约束装置、将磁场和空间约束相结合、双脉冲激发,以及双脉冲激发和空间约束相结合等技术手段来进一步提高激光等离子体的发光强度和分析精度,从而实现进一步提高LIBS的探测灵敏度。经过大量的研究工作,取得的主要研究成果和创新点如下：(1)首次采用新型的铝制半球形腔约束装置应用于单脉冲LIBS分析中,实现了激光诱导冲击波对等离子体的三维均匀压缩效果。该半球形腔空间约束装置不仅可以增强样品中高含量元素的原子光谱,也能增强样品中低含量的元素的原子光谱谱线强度。采用圆筒管型二维约束机构可以使得等离子体强度最佳增强倍数为9倍,而采用该半球形腔三维空间约束装置的最佳光谱增强效果可达12倍,增强效果明显。(2)首次在国内外提出磁场约束与空间约束相结合的LIBS光谱增强方案,设计并研制了磁镜与半球形腔空间约束相结合的磁-空双重约束装置。实验结果表明,该装置能有效实现最佳磁场约束增强与最佳空间约束效果的叠加,达到磁-空混合增强的效果,其最佳增强效果可达24倍。(3)采用双脉冲激发探索了激光双脉冲在不同时间间隔条件下激光等离子体粒子的散射和光谱增强效应,提出了第一束光激发后产生的等离子体冷凝后悬浮于烧蚀坑附近的观点。通过对铝等离子体冷凝后的颗粒再次加热激发后不仅成功改进了A1原子光谱谱线的分辨率,还改进了A1原子谱线线宽,同时,抑制了A1原子光谱谱线的自吸收效应。(4)首次提出将空间约束与双脉冲LIBS相结合的增强方案,并成功将平行面板应用于双脉冲激发的LIBS中,在调整平行面板距离后接着调整两激光脉冲之间的时间间隔,从而获得平行面板空间约束条件下,双脉冲LIBS的最佳增强效果。最佳的增强效果可以达到168.6倍。本论文所研究开发的半球形空间约束,磁-空双重约束以及空间约束与双脉冲LIBS相结合的混合增强技术对激光等离子体的光谱增强效果显著,设计制作简单,成本低,具有十分广阔的发展空间和应用前景。同时也为提高LIBS探测灵敏度提供了一系列全新的研究方法。更多还原

【Abstract】 Laser-induced breakdown spectroscopy (LIBS), which uses focusing a powerful pulsed laser beam onto a sample to create a plasma, by spectrally analyzing the optical emission from the plasma, the element composition and content of the sample could be deduced. The significant attributes of LIBS technique are:ability to detect all elements, simultaneous multi-element detection capability, no need to vacuum, little or no sample preparation, non-destructive to the sample, real-time analysis, in situ diagnosis and remote detection. Therefore, since it was appeared, LIBS technique has been drew widespread attention, and it is developing to one of a valuable spectral analysis technique. Now, successful applications of LIBS has been found in many areas, such as chemical and biological hazards analysis, geological survey, artwork detection and space exploration.However, the poor limit of detection, low precision of analysis, lead to the low detection sensitivity of LIBS, has become the bottleneck of its further development, how to improve the LIBS detection sensitivity, which has become an important research subject in future. The main study of this thesis is using new-style space confinement, magnetic field and space confinement combination, dual-pulse excitation, and dual-pulse excitation and space confinement combination to further improve the optics emission intensity and accuracy of analysis from laser-induced plasma. After lot of research work, the following achievements and points of innovation:(1) The spatial confinement effects using a new-style of aluminium hemispherical cavity in single LIBS analysis were investigated for the first time, for the purpose of realization of three-dimensional uniform compression to the laser-induced plasmas. This hemispherical cavity not only can be used to enhance the atom spectra from high composition elements in the sample, but also used to enhance the low concentration elements. The best enhancement factor for the emission intensities from laser-induced plasmas by using the two-dimensional cylindrical confinement was about9, while a significant enhancement factor of about12was achieved when using three-dimensional hemispherical cavity.(2) The spectral enhancement scheme by combination magnetic field and spatial confinements in LIBS was investigated for the first time, both a magnetic mirror and a hemispherical cavity were designed and made as a magnetic and spatial confinement. The experimental results show that this double confinement can be used simultaneously to magnetically and spatially confine plasmas, and the maximum enhancement factor about24was obtained.(3) The enhancement effects of optical emission and scattering from laser-induced plasma using double-pulse excitation with different interpulse delay time were investigated, the point of the suspended particles on crater was condensed by the plasmas which excited by the first laser pulse was bring forward. By reheating the aluminium particles which formed by the A1plasmas, not only improve the resolution of Al atomic spectra, but also the self-absorption effect of Al amtomic spectra was disappeared.(4) The enhancement scheme of optical emission in Dual-pulse (DP-LIBS) LIBS with spatial confinement was bring forward for the first time, and a pair of plate walls were successfully used to spatially confine the plasmas produced in DP-LIBS, by the optimization of the distance between two Al walls and the interpulse delay time, the maximum enhancement factor about168.6was obtained.The OES of the plasma have been significantly enhanced with the aluminum hemispherical cavity, the magnetic-spatial confinement or the DP-LIBS with spatial confinement. These confinement are easy design, making and with low cost, so they Have a very broad space for development and application prospects. The results of this study provide a series of new pathways in improving the sensitivity of LIBS.更多还原