Formation and initial evolution of nanoparticles at ultrashort laser ablation of gold: molecular dynamics simulation

The formation of nanoparticles at ultrashort laser ablation of gold in vacuum is investigated theoretically. The analyses of the nanoparticle formation mechanisms and their initial evolution are performed on the basis of molecular dynamics (MD) simulation. The study is carried out for Au target irradiated by laser pulses of 100 fs duration at laser wavelengths of 800 nm. The evolution of the ablation process is monitored for time interval of few hundreds of picoseconds. The size distribution of the nanoparticles and their velocity distribution are obtained as a function of the laser fluence. The results indicate that the nanoparticles are formed in the stage of superheated material decomposition and phase explosion and fragmentation are the main mechanisms leading to their formation. The results for velocity and size distributions are compared to the available experimental ones and good agreement is observed.