High shock release in ultrafast laser irradiated metals: Scenario for material ejection

TL;DR

This paper uses numerical simulations to explore how ultrafast laser pulses cause metals to undergo phase changes and material ejection through mechanisms like phase explosion and fragmentation, with implications for laser ablation.

Contribution

It provides a detailed thermodynamic and hydrodynamic analysis of ultrafast laser-metal interactions, highlighting new insights into ejection mechanisms and phase evolution pathways.

Findings

Identification of phase explosion as a key ejection mechanism.

Estimation of recast material size after laser irradiation.

Comparison of mechanical fragmentation with experimental data.

Abstract

We present one-dimensional numerical simulations describing the behavior of solid matter exposed to subpicosecond near infrared pulsed laser radiation. We point out to the role of strong isochoric heating as a mechanism for producing highly non-equilibrium thermodynamic states. In the case of metals, the conditions of material ejection from the surface are discussed in a hydrodynamic context, allowing correlation of the thermodynamic features with ablation mechanisms. A convenient synthetic representation of the thermodynamic processes is presented, emphasizing different competitive pathways of material ejection. Based on the study of the relaxation and cooling processes which constrain the system to follow original thermodynamic paths, we establish that the metal surface can exhibit several kinds of phase evolution which can result in phase explosion or fragmentation. An estimation of the amount of material exceeding the specific energy required for melting is reported for copper and aluminum and a theoretical value of the limit-size of the recast material after ultrashort laser irradiation is determined. Ablation by mechanical fragmentation is also analysed and compared to experimental data for aluminum subjected to high tensile pressures and ultrafast loading rates. Spallation is expected to occur at the rear surface of the aluminum foils and a comparison with simulation results can determine a spall strength value related to high strain rates.