Comparison of supercontinuum laser absorption and emission spectroscopy of Li I 670.8 nm transition in laser-produced plasmas

Optical spectroscopy of laser-produced plasmas is a versatile and rapid platform for elemental and isotopic detection, with applications in energy, nuclear, and defense technologies. In this study, we examine spatially and temporally resolved spectral features of plasmas generated by nanosecond laser ablation of a LiAlO₂ target using two complementary techniques: supercontinuum laser absorption spectroscopy (SC-AS) and laser-induced breakdown spectroscopy (LIBS). All spectra were collected for the Li I doublet centered at ≈[jls-end-space/]670.8 nm with fine-structure transitions at 670.776 nm ( Image 1001 ), 670.791 nm ( Image 1002 ), and 670.806 nm ( Image 1003 ). Spatially and temporally resolved measurements were performed in a reduced pressure ambient gas (0.7 Torr He). A double-echelle spectrograph coupled to an intensified charge-coupled device with resolving power (Formula presented) was used for light detection. Results show that SC-AS resolves the Image 1004 -D₂, Image 1005 -D₂ + Image 1006 -D₁, and Image 1007 -D₁ fine-structure components over a broad temporal window, in contrast to emission spectroscopy. Absorption spectra consistently exhibit narrower linewidths, while emission profiles are broadened and peak heights are modified by self-absorption effects. Time- and space-resolved measurements further show that absorption signals persist at later stages of plasma evolution, where lower temperatures reduce Doppler broadening and improve spectral resolution. Our results highlight the inherent limitations of emission-based isotopic analysis in laser-produced plasmas, while demonstrating that SC-AS offers a viable route to isotope-resolved measurements; nevertheless instrumental broadening remains a fundamental constraint for both approaches.