Near-threshold laser-induced sputtering of aluminum surface by UV and IR irradiation

Abstract

Laser-induced particle emission (Al, Al *, Al +) from Al and Al 2O 3 surfaces irradiated by laser beams at different wavelengths has been examined to investigate primary processes of laser-initiated sputtering. The Nd-YAG (1064 nm, 10 ns, 1–4 J/cm 2), excimer XeCl (308 nm, 10 ns, 0.1–0.5 J/cm 2) lasers or Stokes components of stimulated Raman scattering of XeCl laser radiation in pressed hydrogen (353 nm, 414 nm) were employed for irradiation of the surfaces of the samples in the helium (air) atmosphere at pressures (10 −3–400 Torr). The near-threshold energy fluences on the sample surface did not result in detectable surface damages but changed the surface structure and composition. LIF spectroscopy was used to detect nonemitting ground state species, while excited species were observed by time-resolved optical emission spectroscopy. The role of photochemical (electronic) and thermal effects in the initiation of particle emission have been identified in dependence on the laser wavelength. The predominance of the photochemical mechanism over the thermal one has been established in the initiation of laser-induced sputtering by radiation of excimer XeCl laser. Additionally, the resonant aspects of laser–surface–plume interaction as determined from the resonant and nonresonant irradiation of aluminum at 308.2 nm and 307.8 nm have been discussed.