Femtosecond laser pulse irradiation of solid targets as a general route to nanoparticle formation in a vacuum

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) W/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.