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

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Abstract
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.