The Effect Of Cavity Confinement On Laser-Induced Breakdown Spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) technology is a fast developing analytical atomic spectroscopic technique in recently years. The technology has advantages of rapidity, multi-element analysis simultaneity, real-time, no sample state restriction, micro-loss, remote operation and so on. It has thus been widely used in raw material analysis, analysis in dangerous environments, environmental monitoring and medicine analysis. However, it suffers a relatively poor sensitivity in comparison with other analytical spectroscopy methods, and this has seriously limited its further development. Therefore, a globe effort was focused on how to improve the sensitivity and signal intensity of LIBS. Generally, two methods had been used, one is double-pulse LIBS, including collinear double pulse LIBS, perpendicular double pulse LIBS and cross double pulse LIBS; Another is laser ablation fast pulse discharge plasma spectroscopy, which is analogous to the double-pulse LIBS by utilizing periodic oscillating discharge plasma generation to instead of the second laser beam so as to effectively reheat the laser-induced plasma and then improve the sensitivity, precision and S/N. This technology applies to detection and measurement of various major and trace elements in soil.In recent years, The combination of laser induced plasma and cavity confinement can also effectively improve the LIBS signal quality. However this topic has not been fully studied.:Firstly, most researchers have only studied the effect of plasma confinement on spectral intensity in single pulse LIBS and only use one or limited cavities, No efforts has been done on how about the cavity size will affect the plasma emission. And the optimal cavity size for plasma confinement in LIBS has never been obtained. Further, the effects about the plasma confinement on the stability of plasma emission intensity reported so far were controversial. Secondly, only the combination of a parallel plan cavity confinement with perpendicular double pulse LIBS has been studied and used to improve the signal quality. No research has been done on cavity confined collinear double pulse LIBS technique. Therefore, in this paper, a systematic study on cavity confinement on plasma emission characters in LIBS has been performed.Firstly, a full introduction about the growth of LIBS technology and the current development of cavity confined LIBS technology are presented. The design of the experiment, the experiment instrument and their parameters are provided as well. Then we focus our research on two aspects. (1) Designed and made a series of aluminum cylindrical cavity and combined with signal pulse LIBS. Based on the signal intensity and stability in terms relative standard deviation(RSD), an optimize cavity constraints size has obtained.. Under the optimized cavity size confinement, the effect of cavity confinement on the plasma electron temperature and electron number density are derived, and the quantitative analysis of iron component in aluminum alloy sample was demonstrated with an improved limit of detection(LOD). (2) For the first time, a collinear double pulse LIBS was combined with cavity confinement, and used to evaluate the LIBS signal intensity and stability. After optimize the interpulse delay time, and use the optimized cavity obtained above, a significant improvement of LIBS signal stability and RSD was observed along with higher plasma electron temperature and electricity number density. Finally, all the above studies are concluded and the prospect of the work is given as well.