M. I. Nedelko

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 2 O 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.

Dynamics of the Emission of Light by C2 and C3 Molecules in a Laser Plasma Produced by Two-Pulse Irradiation of the Target

The laser plasma produced by irradiation of a graphite target simultaneously by the first and second harmonics of two Nd3+:YAG lasers has been studied by emission spectroscopy methods. The delay between radiation pulses (τ) varied from 0 to 700 μsec. It is established that in the absence of a delay between pulses (τ = 0) the increase in the intensity of plasma emission at the wavelengths corresponding to the radiative transitions of the C2 and C3 molecules is of nonradiative character. The plasma produced by laser radiation at the wavelength λ = 1064 nm exerts its influence on the radiation spectrum of the plasma produced by laser radiation at the wavelength λ = 532 nm, if the magnitude of the delay between laser pulses τ does not exceed 30 μsec. The most probable reason for this character of influence of the prepulse on the laser plasma radiation spectrum is sublimation of soot particles caused by laser radiation at λ = 532 nm.