Designer pulses for optimal ablation
Abstract
Determining thermodynamic trajectories is an essential factor for controlling the nature and the energetic characteristics of the ablation products following laser irradiation of materials on ultrafast scales. In this respect, designing the energy delivery rate using pulse shaping methods in the temporal domain is a powerful way for controlling the excitation and thermodynamic relaxation of the material and its hydrodynamic advance. Using experimental and theoretical adaptive loops based on hydrodynamic codes we indicate the shapes of optimal pulses on ultrashort and short scales required to reach extreme thermodynamic states at limited energy input. These affect the excitation level and the energetic content of the ablation products, as well as the balance between thermal and mechanical energy, and usually imply light coupling into the incipient material hydrodynamic motion. Consequences are visible in the formation of atomic and cluster species, their kinetics and spectral emissivities, and in the ejection of nanoscale liquid droplets. A discussion on the nature of these resulting exotic thermodynamic states, mostly implying supercritical paths, will be given. The results are interesting for remote spectroscopy applications, e.g. LIBS, resulting ablation quality, and for generation of nanoparticles.