Implementation of kinetics of phase transitions into hydrocode for simulation of laser ablation

TL;DR

This paper models femtosecond laser interactions with metals, analyzing phase transitions, melting, and ablation mechanisms using a comprehensive thermodynamic approach, and correlates simulation results with experimental data.

Contribution

It introduces a detailed simulation framework incorporating metastable phases and nucleation theory for laser ablation of metals, advancing understanding of phase transition dynamics.

Findings

Metastable liquid phases significantly influence ablation outcomes.

Multiple ablation mechanisms are identified, including vaporization and droplet formation.

Simulation results align well with experimental observations.

Abstract

We model an interaction of femtosecond laser pulses (800 nm, 100 fs, 1-100 TW/cm$^2$) with metal targets (Al, Au, Cu, and Ni). A detailed analysis of laser-induced phase transitions, melting wave propagation and material decomposition is performed using a thermodynamically complete two-temperature equation of state with stable and metastable phases. Material evaporation from the surface of the target and fast melting wave propagation into the bulk are observed. On rarefaction, the liquid phase becomes metastable and its lifetime is estimated using the theory of homogeneous nucleation. Mechanical fragmentation of the target material at high strain rates is also possible because of void growth and confluence. In our simulation several ablation mechanisms are observed but the major output of the material is found to originate from the metastable liquid state. It can be decomposed either into a liquid-gas mixture near the critical point, or into droplets at high strain rates and negative pressure. The simulation results correlate with available experiments.