Propagation of a femtosecond pulsed laser ablation plume into a background atmosphere

We investigate the effects of ambient gas on the expansion dynamics of laser plume produced during femtosecond laser ablation of a metallic target. We studied experimentally plume propagation for ambient air pressure ranging from 10(-6) to 50 mbar, observing that the atomic and nanoparticles plume components experience different effects. We interpret these results with a simplified model of the plume front propagation, which is able to fully reproduce the main experimental features. Our results allow us to estimate quantitatively the nanoparticles plume content (up to about 80%), and can help identifying optimal conditions of nanoparticles deposition for thin films production.