Guiding heat in laser ablation of metals on ultrafast timescales: an adaptive modeling approach on aluminum

Abstract

Using an optimal control hydrodynamic modeling approach and irradiation adaptive time-design, we indicate excitation channels maximizing heat load in laser ablated aluminum at low energy costs. The primary relaxation paths leading to an emerging plasma are particularly affected. With impulsive pulses on ps pedestals, thermodynamic trajectories are preferentially guided in ionized domains where variations in ionization degree occur. This impinges on the gas-transformation mechanisms and triggers a positive bremsstrahlung absorption feedback. The highest temperatures are thus obtained in the expanding ionized matter after a final impulsive excitation, as the electronic energy relaxes recombinatively. The drive relies on transitions to weakly coupled front plasmas at the critical optical density, favoring energy confinement with low mechanical work. Alternatively, robust collisional heating occurs in denser regions above the critical point. This impacts the nature, the excitation degree and the energy content of the ablated matter. Adaptive modeling can therefore provide optimal strategies with information on physical variables not readily accessible and, as experimentally confirmed, databases for pulse shapes with interest in remote spectroscopy, laser-induced matter transfer, laser material processing and development of secondary sources.

Ultrafast switching of surface plasmonic conditions in nonplasmonic metals

“…Transient electron and lattice temperatures in W for single ultrashort pulse irradiation ( Fig. 1(b)) are estimated using a two-temperature hydrodynamic code (Esther) [20] which describes the energy balance using Helmholtz optical formalism and electron-phonon relaxation with temperature-dependent transport properties [6,9]. Electronic temperatures on the rising heat cycle can amount to 2.5 × 10 4 K, inducing electron-phonon nonequilibrium up to 3 ps, with the material in solid state for at least 1 ps.…”

First-principles calculations of heat capacities of ultrafast laser-excited electrons in metals

“…The basic underlying assumption in the two-temperature model is that the electron subsystem consists of a thermalized population of a certain amount of electrons, a condition easily fulfilled in ablation processes conditioned by high electronic temperatures [7]. The energy evolution is determined by photon absorption, energy accumulation and thermal/mechanical transport (involving electron-electron and electron-phonon interaction) based on nonequilibrium dynamics.…”

Ab Initio Nonequilibrium Thermodynamic and Transport Properties of Ultrafast Laser Irradiated 316L Stainless Steel

“…The electronic pressure is also of importance as it plays a significantly role in hydrodynamic models. 10 This model is based on the assumption that both ionic and electronic systems can be efficiently described by two separated and effective tem-peratures which is found to be consistent with experimental observations. 11,12 The thermodynamic conditions experienced by the material under irradiations strongly depends on these nonequilibrium properties.…”