Mitigating Self-Absorption/Self-Reversal Effects in Li I Transitions in Laser-Produced Plasmas for Isotopic Analysis

Optical emission spectroscopy of laser produced plasmas is a promising, rapid analysis method for the detection and quantification of Li and its isotopes needed in geochemical, nuclear, and energy storage applications. However, spectral broadening in laser produced plasmas, presence of fine and hyperfine structures, and self-reversal effects make Li isotopic analysis extremely challenging especially at high pressure ambient conditions. The present study explores the influence of Ar, N
2
, and He ambient gases over the pressure range of 0.05 - 100 Torr on line broadening and self-reversal of the Li I transition with the greatest isotopic shift in the VIS spectral region (i.e., ∼670.8 nm, ∼15.8 pm isotopic shift). We perform spatially and temporally resolved optical emission spectroscopy of plasmas produced via laser ablation of LiAIO
2
substrates. In addition, complementary monochromatic imaging and spatially-integrated emission spectroscopy was performed to understand the differences in Li I emission intensity as a function of ambient gas and pressure, and its relation to self-reversal effects. Our results show that the self-reversal and linewidth is reduced at lower pressures for all gases, and using optimized plasma conditions with chemometric methods, the
⁶
Li/
⁷
Li isotopic ratios can be predicted [1].