Interaction of short and intense laser pulses with dielectric materials: from absorption to ablation

Abstract

Modeling of the interaction of short laser pulses with dielectric materials is addressed. Based on phenomenological considerations, it is shown how the transition from primary absorption to ablation takes place. This description is illustrated by two particular examples allowing to highlight specific physical phenomena. An accurate estimate of the early absorption, which strongly depends on material characteristics, is shown to play an important role. An approach to evaluate this early absorption is presented. With the development of short and intense laser pulses, laser modifications of materials for various applications become possible. Such modifications are due to energy absorption which ultimately leads to ablation for the highest laser intensities. The design of specific nano-structures requires both the knowledge and the modelling of physical mechanisms responsible for these material modifications. In this presentation, we focus on dielectric materials. In that case, briefly, the physical processes which may lead to material modifications are the following: ionization (electron transition from the valence band to the conduction band), heating of conduction electrons, energy transfer from electrons to the lattice, material response relying mainly on hydrodynamics (1). Regarding the electron dynamics, it can be described in terms of collisions including the electron-photon, electron-ion-photon, electron- phonon-photon, electron-ion, electron-phonon, and electron-electron collisions (2). Based on this general phenomenology, we will consider two particular examples under simplified conditions in order to highlight specific mechanisms. The fist study is devoted to the evolution of surface damage and ablation of silica with respect to the pulse duration within the sub-picosecond timescale. This study exhibits the role of various ionization mechanisms depending on the pulse duration. The second study is devoted to the interaction of sub- picosecond laser pulses with dielectric nanoparticles embedded in optical materials. It exhibits the influence of possible laser field enhancement leading to a strong nonlinear increase in the density of conducting electrons even without impact ionization.