Nanoparticle formation by femtosecond laser ablation

The main features of ultra-short laser ablation of various materials (metals, semiconductors or insulators) have been studied through the complementary analyses of the plasma plume induced by laser irradiation, and of the deposited films. The generation of nanoparticles (in the 10-100 nm range) was observed and these findings were investigated in order to obtain information on the relevant parameters governing the formation of these nanoparticles. By the use of polyatomic targets, the non-congruent formation of nanoparticles was evidenced, demonstrating the existence of complex phenomena (phase separation, chemical reactions and interaction with the residual gas) during the laser-matter interaction and plasma expansion. An unexpected finding was the influence of the laser beam spot size on nanoparticle emission during femtosecond laser ablation. The comparison of these results with the currently admitted explanations of ultra- short laser-matter interactions clearly indicates that the existing models and simulations do not describe or explain the overall phenomena taking place during femtosecond laser ablation, and another approach has to be envisaged including the influence of the parameters evidenced in this work.