Two-temperature molecular dynamics simulation study of copper thin film irradiation with femtosecond and picosecond laser pulses

Metal targets irradiated with laser pulses have a wide range of applications in thin film preparation, nanomaterial synthesis, bio-medical imaging, and metal ablation. Here, using two-temperature model based molecular dynamics simulation, we investigate laser mediated ablation in copper. Ablation of the film starts with the formation of voids within it. This void forming mechanism at low laser fluences (≤100 mJ/cm2) is studied using both picosecond and femtosecond pulses. At the same fluence, shorter laser pulse transfers more energy to the atoms generating temperatures greater than the melting temperature of the crystal. This increases the kinetic energy of the atoms and they start vibrating with different velocities. If these vibrations cross a threshold of 5 Å per picosecond (500 m/s), voids and faults start appearing in the system. At the same fluence, higher concentration of voids are also created at a faster rate with the femtosecond pulse.