Laser-induced Breakdown Spectroscopy (LIBS) is a spectrometry based on laser plasma emission. It can realize rapid, remote, and in-situ detection for almost any materials in open air. LIBS assisted with laser-induced fluorescence (LIBS-LIF) is a promising enhancement method for LIBS. In LIBS-LIF, a wavelength-tunable laser beam focuses onto plasma to resonantly excite specific atoms. When the laser wavelength is equal to an excited line of a target element, the atoms of the target element absorb laser photons, and then emit strong atomic fluorescence. Under ideal conditions, no spectral lines from matrices were close to the excited lines from the target elements. Only target atoms would absorb the excitation laser energy, and then the analytical sensitivity is effectively improved. Practically, when excited lines of matrix and target elements are very close, a large number of matrix atoms absorb too much laser energy; and then the laser energy absorbed by the atoms of target elements lessens, resulting in lower excitation efficiency and less improvement of analytical sensitivity.
The laser spectroscopy team in Wuhan National Laboratory for Optoelectronics discovered various distributions of different elements in plasmas. Based on this discovery, spatially selective excitation was proposed to improve excitation efficiency in laser-induced breakdown spectroscopy combined with laser-induced fluorescence (LIBS-LIF). Taking chromium (Cr) and nickel (Ni) elements in steels as examples, it was discovered that the optimal excitation locations were the center of the plasmas for the matrix of the iron (Fe) element but the periphery for Cr and Ni elements. By focusing an excitation laser at the optimal locations, not only excitation efficiency but also the analytical sensitivity of LIBS-LIF were improved by 5 and 10 times on LoDs, respectively. This study provides an effective way to improve LIBS-LIF analytical performance.
This work was financially supported by Major Scientific Instruments and Equipment Development Special Funds of China (No. 2011YQ160017) and National Natural Science Foundation of China (61575073), which has been published on the journal of Optics Express with the title of “Spatially selective excitation in laser-induced breakdown spectroscopy combined with laser-induced fluorescence”.
Enclose：Jiaming Li, Zhongqi Hao, Nan Zhao, Ran Zhou, Rongxing Yi, Shisong Tang, Lianbo Guo, Xiangyou Li*, Xiaoyan Zeng, Yongfeng Lu, Spatially selective excitation in laser-induced breakdown spectroscopy combined with laser-induced fluorescence ,Optics Express, 2017, 25(5), 4945-4951
Fig.1. The scanning intensity maps excited by Cr I 357.87 nm (a) and Ni I 234.56 nm（b）in laser-induced plasma on low-alloy steels