Effect of Plane Mirrors Combined with Au-Nanoparticle Confinement on the Spectral Properties of Fe Plasma Induced by Laser-Induced Breakdown.

To overcome the shortcomings of low detection sensitivity and high spectral line background noise of traditional laser-induced breakdown spectroscopy (LIBS), a method of combining flat mirrors with gold nanoparticles (Au-NPs) was proposed. First, independent plane mirror and Au-NPs experiments were performed by using aluminum alloy samples. After that, the samples were placed under four conditions (None-LIBS; Three mirrors-LIBS; 20 nm Au-NPs-LIBS; 20 nm Au-NPs and Three mirrors-LIBS), and the differences between various spectral parameters were analyzed. The experimental results show that the optimal number of plane mirrors is 3, and the optimal size of gold nanoparticles is 20 nm. When 20 nm Au-NPs and Three mirrors are used in combination, the plasmonic spectral intensity can be effectively enhanced. The enhancement factor is up to 2.98 (Fe II 240.45 nm), and the signal-to-noise ratio (SNR) is significantly improved up to 10.03. The variation of the plasma temperature between 1 and 5 μs was also investigated, and the experimental results showed that the plasma temperature could be increased by the flat mirror, while the electron temperature was almost unchanged under the action of Au-NPs. It is shown that the combination of the two enhancement methods can effectively increase the spectral intensity and improve the signal-to-noise ratio, which will help to improve the detection performance of the LIBS system.