| Femtosecond laser ablation is an important process in the micromachining and nanomachining of microelectronic, optoelectronic, biophotonic and MEMS components. The process of laser ablation of silicon is being studied on an atomic level using molecular dynamics (MD) simulations. We investigate ablation thresholds for Gaussian laser pulses of 800 nm wavelength, in the range of a few hundred femtoseconds in duration. Absorption occurs into a hot electron bath which then transfers energy into the crystal lattice. The simulation box is a narrow column 5.4 nmx5.4 nmx81 nm with periodic boundaries in the x and y transverse directions and a 1-D heat flow model at the bottom coupled to a heat bath to simulate an infinite bulk medium corresponding to the solid bulk material. A modified Stillinger-Weber potential is used to model the silicon atoms. The calculated ablation thresholds of silicon are compared to values reported in experimental and theoretical studies. We obtain reasonable agreement with experiment for pulse lengths of 100 fs and 200 fs (1/e) giving thresholds of 0.13 J/cm2 and 0.19 J/cm 2, respectively. The ablation threshold is found to have a square-root dependence on the pulse length. |
