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.