Synergy enhancement and signal uncertainty of magnetic-spatial confinement in fiber-optic laser-induced breakdown spectroscopy

Abstract

The synergy enhancement of magnetic-spatial confinement using a bar magnet pair was applied to fiber-optic laser-induced breakdown spectroscopy (FO-LIBS). By studying the plasma morphology and emission spectroscopy, the plasma temporal behaviors under free expansion, spatial confinement, and magnetic-spatial confinement have been carefully compared. Temperature distribution and pixel-to-pixel relative standard deviation (RSD) of plasma morphology under the combined effect of magnetic field and the reflected shock wave on fiber-optic laser-induced plasma were studied for the first time. The magnetic field was found to deform the plume mainly at the left and right sides, and the two high-intensity areas in FO-LIBS plasma rose from 8.7% to 13.8% and resisted being compressed together after the shock wave reflected. The magnetic-spatial confinements also demonstrated better enhancements in emission spectra than only spatial confinement, and the magnetic field tended to give around 20% and 50% additional enhancement on line intensity at the early and later stages of evolution, respectively. Besides, the self-reversed effect was significantly reduced in magnetic-spatial confinement, which can be explained by more evenly distributed temperatures calculated by spatially resolved spectra. Pixel-to-pixel RSD distribution of plasma morphology was studied, and it was found that the area of more fluctuated parts was reduced by 40% and concentrated on the left and right sides of the plasma in the magnetic field at the early stage. After the shock wave passed through, the two high-intensity areas were observed to fluctuate less due to the compression of the shock wave. Furthermore, shot-to-shot spectra fluctuation was also reduced by up to 50% under the magnetic-spatial confinement, which is consistent with the results of plasma morphology fluctuation. This study provides evidence of plasma emission signal enhancement and stabilization under magnetic-spatial confinement in the FO-LIBS system.