Laser-induced breakdown spectroscopy (LIBS) is an element analysis technique with advantages of rapid, in situ, real-time, nearly nondestructive nature, no or simple sample preparation, simultaneous multielemental detection and remote sensing capability etc. However, the self-absorption seriously interferes the emission spectrum of laser-induced plasma and destroys the linear mapping relationship between spectral intensity and elemental concentration, especially when the self-absorption is serious, the spectral line has a dip in the center (called self-reversal). The accuracy and sensitivity of quantitative analysis are seriously affected.
To reduce the serious influence of the self-absorption effect in LIBS, Associate Prof. Lianbo Guo has been exploring the intrinsic physical properties of the plasma to eliminate the self-absorption effect. In 2015, the research group proposed a method of laser-stimulated absorption LIBS (LSA-LIBS) to prevent self-absorption in the open air. It can effectively reduce the self-absorption effect in LIBS. The related results are published in t in Optics Letter (J. M. Li, L. B. Guo*, et al. "Reduction in laser-induced breakdown spectroscopy using laser-stimulated absorption", Opt. Letters 40 (22), 5224-5226 (2015)), but this method also has some limitations, such as the need to predetermine the types of the elements to be measured and the related parameters of their energy states, at a time only one spectrum line of one element can be analyzed. The method cannot satisfy the industrial application, due to the device used is sensitive to the environment. Then, is there a new method of reducing the self-absorption effect for multiple elements simultaneously within a wide spectral range, and the device has the advantages of simple operation, small size, strong environment adaptability, simple maintenance and low price, and so on. If so, it can completely solve the interference problem of LIBS self-absorption effect from the source, and really break through the bottleneck of quantitative analysis of LIBS technology.
The research group of Wuhan National Laboratory for Optoelectronics proposed to reduce multielemental self-absorption within a wide spectral range (200-900 nm) by using microwave-assisted excitation in LIBS (MAE-LIBS). Self-absorption reduction of sodium (Na), potassium (K), aluminum (Al), silicon (Si), and calcium (Ca) in potassium feldspar using MAE-LIBS was investigated. The mechanisms of self-absorption reduction in MAE-LIBS were also investigated. The results show that the serious self-absorption of spectral lines (Na and K) was reduced. The full widths at half maximum (FWHMs) of Na I 589.0 nm, Na I 589.6 nm, K I 766.5 nm, and K I 769.9 nm in potassium feldspar were reduced by 43%, 43%, 53%, and 47%, respectively. The results confirmed that MAE-LIBS is capable of reducing the self-absorption effect for multiple elements simultaneously. Moreover, microwave generators are compact and economical. This work shows great potential and feasibility for MAE to improve LIBS analyses.
On May 1, 2018, " Multielemental self-absorption reduction in laser-induced breakdown spectroscopy by using microwave-assisted excitation" was published online in Optics Express.
The research was financially supported by National Natural Science Foundation of China (No. 61575073 and 51429501). Associate Prof. Lianbo Guo is the corresponding author of the paper, Prof. Yongfeng Lu, Xiaoyan Zeng, Xiangyou Li, and Jun Duan give guidance, and Ph.D. candidate Yun Tang is the first author, postdoctoral candidate Hao Zhongqi and Tang Shisong, Ph.D. candidate Li Jiaming, and M. S. candidate Zhu Zhihao are co-authors.
Fig.1. Boron LIBS-LIRF principle (a) and spectral enhancement (b).
