Numercial Studies of Ultra-Short Laser Interactions: Application for Nanotechnology
Résumé
Better understanding of ultra-short laser interactions requires two-temperature modeling of laser energy absorption and its following relaxation. In particular, two-temperature hydrodynamic model with a thermodynamically complete equation of state provide insights into the ablation mechanisms are observed. For metal targets, the major fraction of the ablated material is found to originate from the metastable liquid region, which is decomposed either thermally or mechanically. In addition, effects of the ultra-short laser excitations on semiconductors and wide band gap materials require particular attention. In this case, material ionization through multi-photon excitation and electron-impact ionization should be considered. These processes are modeled by using a detailed kinetic approach. Laser-irradiated material response is based on the electron-phonon/ion interactions, which in turn depend strongly on the energy of the electron sub-system defined by laser parameters and on the material properties. In this study, based the numerical modeling, we propose the energy-based analysis of these interactions. Single, double and multiple shot interactions are simulated with a particular focus on the control over the transient reflectivity changes and the energy deposition rate. We show that the history of laser excitations affects not only the ionization process and the final number of the conduction band electrons, but also determines the rate of the energy deposition into the material.