Ultrashort laser ablation of solid matter in vacuum: a comparison between the picosecond and femtosecond regimes

We have investigated the main features of ultrashort laser ablation of solid matter by using laser pulses of different durations, ranging from fs to ps timescales, and wavelengths, in the visible-near infrared spectral range. The analysis has been carried out on Si and Ni in terms of the two main characteristics of the ablation process: vacuum expansion of the ablated material and generation of nanoparticles of the target material. Fast photography and optical emission spectroscopy were used to characterize the plume expansion dynamics, while atomic force microscopy analysis of less than one layer deposits was employed to analyse the size distribution of the produced nanoparticles. Our analysis indicates that the properties characterizing the plume expansion in vacuum as well as the size distribution of the nanoparticles produced with laser pulses in the range of 100 fs-1 ps are almost independent of the specific material properties and laser pulse characteristics, thus representing general features of the process in these conditions.