We present a detailed investigation of the temporal evolution of line and continuum emissions in laser-induced breakdown spectroscopy (LIBS) of gaseous uranium hexafluoride (UF6), focusing on the spectral region near 646 nm. Spectral emission features, signal-to-background ratios (SBRs) of selected uranium lines, and spectral linewidths were examined under varying UF6 pressures (15–60 Torr) and laser pulse energies (10–60 mJ). Higher pressures and pulse energies enhanced continuum emission and reduced SBRs but did not cause significant spectral congestion. Additional studies with the use of different laser systems, including nanosecond-pulsed Nd:YAG lasers (at fundamental and various harmonics) and a femtosecond-pulsed Ti:sapphire laser, revealed long-lived plasma continua in all cases. This persistent continuum is attributed to a pseudo-continuum from overlapping molecular emissions, as its intensity scales linearly with electron number density, deviating from the expected quadratic dependence of classical ion–electron interactions for free-free and free-bound continuum emission. Based on plasma persistence time, SBR, U II/U I intensity ratios, and electronic excitation temperature, no fundamental advantage was found for femtosecond-pulsed lasers over conventional nanosecond-pulsed ones for UF6 enrichment assay with direct LIBS measurement.
BT - Spectrochimica Acta Part B: Atomic Spectroscopy DA - 02/2026 DO - 10.1016/j.sab.2025.107357 N2 -We present a detailed investigation of the temporal evolution of line and continuum emissions in laser-induced breakdown spectroscopy (LIBS) of gaseous uranium hexafluoride (UF6), focusing on the spectral region near 646 nm. Spectral emission features, signal-to-background ratios (SBRs) of selected uranium lines, and spectral linewidths were examined under varying UF6 pressures (15–60 Torr) and laser pulse energies (10–60 mJ). Higher pressures and pulse energies enhanced continuum emission and reduced SBRs but did not cause significant spectral congestion. Additional studies with the use of different laser systems, including nanosecond-pulsed Nd:YAG lasers (at fundamental and various harmonics) and a femtosecond-pulsed Ti:sapphire laser, revealed long-lived plasma continua in all cases. This persistent continuum is attributed to a pseudo-continuum from overlapping molecular emissions, as its intensity scales linearly with electron number density, deviating from the expected quadratic dependence of classical ion–electron interactions for free-free and free-bound continuum emission. Based on plasma persistence time, SBR, U II/U I intensity ratios, and electronic excitation temperature, no fundamental advantage was found for femtosecond-pulsed lasers over conventional nanosecond-pulsed ones for UF6 enrichment assay with direct LIBS measurement.
PB - Elsevier BV PY - 2026 EP - 107357 T2 - Spectrochimica Acta Part B: Atomic Spectroscopy TI - Spectral emission characteristics near 646 nm and plasma properties of laser-induced plasma of gaseous uranium hexafluoride UR - https://doi.org/10.1016/j.sab.2025.107357 VL - 236 SN - 0584-8547 ER -