By studying the fs laser produced plume of different materials we show experimentally that the process of matter removal during ultrashort (fs) laser pulse irradiation followed by vacuum expansion is characterized by a number of general features, whichever the nature of the target material. In particular, fs laser ablation of solid targets at laser intensities of the order of ${10}^{12}-{10}^{13}\mathrm{W}∕{\mathrm{cm}}^2$, inevitably leads to the generation of nanoparticles of that material. This has been evidenced by atomic force microscopy analysis of less than one layer deposits showing that the produced nanoparticles have mean radii generally in the range 5–25 nm, with pretty narrow size distributions. These results are in very good agreement with the physical description and numerical predictions of recently published theoretical analyses of fs ablation processes.

We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies.

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields.