Infrared and ultraviolet laser ablation mechanisms of SiO

Abstract

The mechanisms of SiO ablation have been investigated at laser wavelengths in the infrared, at 10.53 μm, and in the ultraviolet at 248 nm. The energy content of the SiO molecule in the plume and the occurrence of phase transformations in the target, are studied as a function of wavelength and fluence of the ablation laser. At 10.53 μm, in the range of fluences of 0.6–3.0 J cm-2, time distributions of ejected SiO, measured at different distances above the surface target are characteristic of thermal ablation, yielding estimated temperatures of the surface in the range from 1300 to 4800 K. The energy channelled as rotational excitation of ejected SiO, scales with increasing fluence. The time distributions of SiO in the plume, obtained at 248 nm laser ablation, are measured at different distances above the target, yielding velocity and energy distributions that shift towards higher values with distance and show a weak tendency to decrease with increasing laser fluence. Raman analysis of the postablated SiO targets irradiated at 10.53 μm, at fluences above 0.6 J cm-2, shows the formation of Si nanocrystals whose size increases with fluence. Phase transformation is not observed at the shorter laser ablation wavelength.