Ablation of dielectrics and metals with ultrashort laser pulses

Few-optical-cycle laser pulses are a key tool in the field of laser-matter interaction, whether for fundamental research or industrial applications. In this context, we study the surface ablation of metals (aluminum, copper, nickel and tungsten) and dielectric materials (fused silica and sapphire) for pulse durations ranging from 15 to 100 femtoseconds and intensity ranging from 10¹² to 10¹⁵ W/cm². The evolution of the ablation threshold is measured, using single-shot, for all materials as a function of the pulse duration. Then, we perform an energy balance experiment over a wide range of fluence (0.1 to 10 J/cm²), giving access to the evolution of the reflected, transmitted and absorbed energy fractions. In metals, at low excitation levels, the comparison between experimental results and modeling (Drude-Lorentz, two-temperature model) highlights the importance of considering the electronic density of states. In particular, inter-band collisions are taken into account with the Drude-Lorentz model, and the non-thermalized electronic population is included in the calculation of the electronic collision frequency (for copper and nickel). We then show that, at high excitation levels, Drude model can be applied to all metals. The energy balance measurement performed on dielectric materials allows the development of a scenario describing the importance of absorption mechanisms and the characteristics of the plasma generated over the whole fluence range. We show that for dielectrics, using the shorter pulses reduces the volume of absorption of the laser energy and improves the ablation efficiency. (author)