Material decomposition mechanisms in femtosecond laser interactions with metals

TL;DR

This study uses numerical hydrodynamics to analyze how femtosecond laser pulses cause material decomposition in metals, revealing mechanisms like thermal and mechanical fragmentation and explaining experimental observations.

Contribution

It introduces a detailed thermodynamic model with phase states and nucleation theory to elucidate femtosecond laser ablation mechanisms in metals.

Findings

Major ablation from metastable liquid decomposed thermally or mechanically.

Metastable liquid state persists and decomposes into droplets and chunks.

Results align with experimental observations of laser ablation.

Abstract

A numerical hydrodynamic study of femtosecond laser ablation is presented. A detailed analysis of material decomposition is performed using a thermodynamically complete equation of state with separate stable and metastable phase states and phase boundaries. The lifetime of the metastable liquid state is estimated based on the classical theory of homogeneous nucleation. In addition, mechanical fragmentation of the target material is controlled based on available criteria. As a result, several ablation mechanisms are observed. A major fraction of the ablated material, however, is found to originate from the metastable liquid region, which is decomposed either thermally in the vicinity of the critical point into a liquid-gas mixture, or mechanically at high strain rate and negative pressure into liquid droplets and chunks. The calculation results explain available experimental findings.