Cluster formation dynamics in a locally-confined gas layer mixed with the plume ablated by pulsed laser irradiation

The dynamical process of pulsed laser ablation is investigated by means of Monte Carlo simulations in order to develop a new cluster source. The interaction between the ablated Cu vapor plume and the He ambient gas induces strong shock compression of the gas by which the gas density is one order of magnitude increased and forms a stable gas layer mixed with the plume at the contact front. It is found that even with the target-wall distance as short as about 80 μm, a mixed layer more than 10 μm in thickness can be formed at about 15 μm away from the source wall. This layer can be locally-confined for a considerable long time of hundreds of ns. Frequent collisions occur among the atoms of vapor and gas within the confined layer which induce effective cluster aggregation. The thermodynamic state of this region is well defined, so that the mono-dispersed growth condition might form cluster beam with well-defined internal freedom.