Figure 2

(a) Schematic of single nanoparticle formation under dual-wavelength fs laser irradiation from a Au film on a dielectric/semiconductor substrate. (b) SEM images of the concentric structures and Au nanoparticles on Si substrate fabricated by dual-wavelength fs laser irradiation of a 30-nm Au film at pulse energies of 0.012 and 0.024 μJ. (c) Array of Au nanostructures fabricated by this method and visualized with DF microscopy; the pulse energies were 0.021 μJ and 0.026 μJ for the upper panel and lower panel, respectively.