Characterization and analysis of the CO₂ laser‐induced ablation of lithium target via laser‐induced fluorescence and absorption spectroscopy of emitted atoms

Pulsed CO₂ laser‐induced ablation of solid lithium is studied in the low‐energy‐density regime where no plasma forms on the surface. Li atoms emitted from the surface are characterized using laser‐induced fluorescence and absorption spectroscopy. Atom densities measured as a function of time for different distances from the surface are well described by a full‐range Maxwellian in a center‐of‐mass coordinate system. For 0.9 J/cm² incident energy density (a fraction being absorbed), the beam velocity and the characteristic temperature are 3×10⁵ cm/s and 8500–10 000 K, respectively. Under these conditions, the number of ablated atoms is about 5×10¹¹ per laser shot. The determined effective beam temperature is much higher than the boiling point of pure lithium. This could be explained considering that a film of oxide with greater vaporization temperature is always present on the surface even in relatively good vacuum conditions.