Theoretical Models and Qualitative Interpretations of Fs Material Processing

Abstract : In this paper a number of numerical models are presented which have been developed to describe the processes taking place at different time and length scales in the different classes of materials under the irradiation by ultrashort laser pulses. A unified drift-diffusion approach for modeling charge-carrier transport in metals, semiconductors, and dielectrics allows to elucidate the dynamics of the electric field generated in the target due to photo-emission and to get insight into the origin of the Coulomb explosion process. The widely known two-temperature model is used to follow thermodynamic paths of irradiated matter and to analyze its phase transformations. Being modified for semiconductors, this model has allowed to establish the nature of high-energetic ion emission using laser pulse tailoring and to undertake a first simplified modeling of ultrafast melting of silicon. A two-dimensional model of dielectric breakdown has made possible to uncover the mechanisms which enable the spatial modulation of the structures induced by temporally modulated laser pulses in wide-band-gap dielectric materials. A combined thermal/elasto-plastic model has provided a deep insight into the mechanisms and dynamics of the microbump and nanojet formation on nanosize gold films under femtosecond laser irradiation.