Numerical analysis of crater formation and ablation depth in thin silicon films heated by ultrashort pulse train lasers

Abstract

This study numerically investigates the optical and heat transfer characteristics of thin silicon films irradiated by ultrashort (shorter than 10 ps) pulse train lasers. The one-dimensional two-temperature model (lDTTM) is extended to the two-dimensional (2DTTM) model for estimation of crater formation. In addition, the wave interference effects on the optical and energy transfer characteristics are considered to predict accurately the energy absorption rates in thin silicon films irradiated by picosecond-to-femtosecond pulse train lasers. Unlike bulk silicon, a significant change in energy absorption is found to occur in thin silicon films with the variation of film thickness due to the wave interference. The spatial distributions of energy carrier and lattice temperature show quite a different tendency at different pulse durations as well as the number of pulses because of significant changes in the optical and thermal properties.The predicted crater shapes and the ablation depths by 2DTTM are also presented.

Thermal and non-thermal ablation mechanisms in crystalline silicon by femtosecond laser pulses: classical approach of the carrier density two temperature model

“…Here, a quite different tendency was observed in the carrier density, lattice temperature, and electron temperature [15] because the ablation threshold is decreased by the number of pulses [20]. To reduce the effect of heat accumulation, a femtosecond burst with a THz repetition rate was used, where the temporal separation between the pulses was in the order of carrier-lattice interaction time [25,26]. Moreover, for single pulse ablation depth determination, many pulses are applied to the material, and the crater depth was divided by the number of pulses [17] but technically involves uncertainties because of the change in the optical characteristics of the material by each pulse [27].…”