Non-Equilibrium Thermodynamics and Formation of Nanoparticles in Femtosecond Laser Ablation

High intensity femtosecond laser ablation processes are computed by molecular dynamics (MD) simulations. The procedure of MD modeling and related numerical techniques are introduced. The volumetric phase separation is illustrated. The emphasis is to understand the thermodynamic state of a material which is heated with an extremely high heating rate, and the formation of particles with nanometer size in the laser-ablated plume. It is revealed that nanoparticles are originated from expansion of a supercritical fluid in a reduced temperature and pressure environment. The parameters of the nanoparticles (temperature, size and velocity) are shown. The results will help to understand femtosecond laser materials processing and applications where nanoparticles are of interest.