Ultrashort-pulse laser irradiation may melt the target and, at higher intensities, lead to ablation. The state
of the material shortly after irradiation is characterized by high temperatures and pressures (both tensile and
compressive). In addition, the material may not yet be in thermal equilibrium. Molecular dynamics simulation
is well suited to model the state of matter under these conditions. We give several examples of how molecular
dynamics simulations have contributed to understanding the ablation phenomena after ultrashort-pulse laser
The motion of both Lennard-Jones solids and metals induced by ultrashort laser irradiation near the ablation threshold is
investigated by molecular dynamics simulation. The universality of the ablation threshold fluence with respect to the
cohesion energy of solids irradiated by femtosecond laser pulses is demonstrated for Lennard-Jones solid and metals
simulated by many-body EAM potentials.
The physical mechanisms and processes underlying the erosion of a surface induced by cluster bombardment or
short-pulse laser irradiation are highlighted. When the average energy delivered per atom in the vicinity of the
surface becomes comparable to the cohesive energy of the solid, sputtering from a so-called spike may result.
Such a spike leads to abundant sputtering (surface erosion) and crater formation. Direct atomization in the
region of highest energy deposition, as well as melt flow and gas flow contribute to the erosion.
The materials phenomena occurring after ultra-fast laser irradiation of a metal in the ps- or fs-regime are
reviewed. With increasing laser fluence, the film melts, voids are formed, the film tears (spallation), and finally
fragments to form a multitude of clusters. These processes are universal in the sense that they occur in widely
differing materials such as metals or van-der-Waals bonded materials. We investigate a Lennard-Jones solid as
well as four different metals (Al, Cu, Ti, W), which vary widely in their cohesive energy, melting temperature,
bulk modulus, and crystal structure. When the energy transfer starting the process is scaled to the cohesive
energy of the material, the thresholds of these processes adopt similar values.
A comparison of the similarities and differences of the mechanisms underlying surface erosion under cluster
ion impact and ultrafast laser irradiation will be drawn.