An Electrohydrodynamics Model for Non-equilibrium Electron and Phonon Transport in Metal Films after Ultra-short Pulse Laser Heating

TL;DR

This paper introduces an electrohydrodynamics model derived from Boltzmann transport equations to accurately simulate non-equilibrium electron and phonon transport in metal films after ultra-short laser pulses, improving upon the two-temperature model.

Contribution

The paper develops a new electrohydrodynamics model that better captures nonlinear thermal transport phenomena in laser-heated metal films compared to existing models.

Findings

The electrohydrodynamics model predicts electron temperature more accurately.

It reveals limitations of the two-temperature model in nonlinear regimes.

The model is computationally more efficient than coupled Boltzmann equations.

Abstract

The electrons and phonons in metal films after ultra-short pulse laser heating are in highly non-equilibrium states not only between the electron sub-system and the phonon sub-system but also within the electron sub-system. An electrohydrodynamics model consisting of the balance equations of electron density, energy density of electrons, and energy density of phonons is derived from the coupled non-equilibrium electron and phonon Boltzmann transport equations to study the nonlinear transport phenomena, such as the electron density fluctuation and the transient electrical current in metal films, after ultra-short pulse laser heating. The time-dependent temperature distributions is calculated by the coupled electron and phonon Boltzmann transport equations, the electrohydrodynamics model derived in this work, and the two-temperature model for different laser pulse durations, film thicknesses, and laser fluences. We find that the two-temperature model overestimates the electron temperature at the frontsurface of the film and underestimates the damage threshold when the nonlinear thermal transport of electrons is important. The electrohydrodynamics model proposedin this work could be a more accurate prediction tool to study the non-equilibrium electron phonon transport process than the two-temperature model and it is much easier to be solved than the coupled electron and phonon Boltzmann transport equations.