Investigating the influence of spatial confinement on self-absorption effects in laser-induced breakdown spectroscopy

Abstract

This study investigates a spatial confinement approach utilizing cylindrical cavities to mitigate plasma self-absorption effects in laser-induced breakdown spectroscopy (LIBS)—a critical limitation for quantitative analysis. Experiments systematically evaluate atomic lines (Al I 396.15 nm, Cu I 521.83 nm, and Mg I 517.27 nm) and an ionic line (Mg II 293.65 nm) of the 6061 Al alloy, T2 Cu, and AZ31B Mg alloy. Results demonstrate that confinement reduces self-absorption through three mechanisms: restricting plasma expansion, elevating the electron temperature, and reducing the ground-state particle density. Optimal reduction occurs at a cavity height of h = 12 mm and a radius of r = 8 mm. Specifically, ionic lines (e.g., Mg II 293.65 nm, ionization energy = 8.65 eV) exhibit significantly stronger reduction than atomic lines under identical conditions, which is attributed to their higher ionization energies and narrower spectral widths. This differential response originates from the reduced ground-state particle density and complex transition pathways in ionic species. The technique effectively minimizes spectral line attenuation and broadening, thereby providing physical insights into the confinement-mediated mitigation of self-absorption and offering a potential strategy for improving quantitative LIBS analysis.