The mechanisms of ultrashort pulsed laser ablation of polycrystalline diamond (PCD) are investigated by means of molecular dynamics simulations. The simulation model provides a detailed atomistic description of the laser energy deposition to the PCD specimen, which is verified by an experiment using 300 fs laser irradiation of a typical PCD sample. It is found that non-homogeneous melting initiates from grain boundaries composed by sp2 hybridized denser diamond-like amorphous carbon atoms of higher potential energies. Furthermore, the interplay of the photomechanical spallation and evaporation is found to be accounted for the material removal in the laser ablation. The laser ablation-induced microstructure changes of the sample are characterized in detail. Simulation results suggest that the sample after laser ablation consists of four zones of different structural lattices. It is found that the top layer of the ablated surface composed by amorphous carbon with abundant vacancies can be wiped off from the surface easily, which agrees well with experimental results.
Keywords: Polycrystalline diamond, laser ablation, molecular dynamics, grain boundary.