An analysis of the dependence on photon energy of the process of nanoparticle generation by femtosecond laser ablation in a vacuum

The dependence on laser wavelength of the process of nanoparticle generation by ultrashort laser ablation of solid matter in a vacuum has been investigated both experimentally and theoretically. The study has been carried out for a Ni target by using laser pulses of ≈300 fs duration at two different laser wavelengths: in the visible (λ = 527 nm) and ultraviolet (λ = 263 nm), respectively. The size distribution of the nanoparticles, which is quite broad in the case of visible light, becomes significantly narrower and slightly shifts towards smaller sizes for ultraviolet light. Molecular dynamics simulations confirm the dependence of the process on the laser wavelength by showing that the laser photon energy affects the material relaxation and, thus, the nanoparticle generation process. This, in turn, indicates that the photon energy can be used as an effective parameter to control the nanoparticle size distribution in femtosecond laser ablation of solid matter.