An adaptive model for the optical properties of excited gold

TL;DR

This paper presents a semi-analytical model for the temperature-dependent optical properties of gold, capturing intraband and interband responses and applicable to ultrafast laser excitation scenarios.

Contribution

It introduces a temperature-dependent Drude-Lorentz model based on density functional theory data, adaptable to other materials and nonequilibrium conditions.

Findings

Intraband response increases with electron temperature

Interband component decreases with electron temperature

Model aligns well with DFT calculations for gold reflectivity

Abstract

We study the temperature-dependent optical properties of gold over a broad energy spectrum covering photon energies below and above the interband threshold. We apply a semi-analytical Drude-Lorentz model with temperature-dependent oscillator parameters. Our approximations are based on the distribution of electrons over the active bands with a density of states provided by density functional theory. This model can be easily adapted to other materials with similar band structures and can also be applied to the case of occupational nonequilibrium. Our calculations show a strong enhancement of the intraband response with increasing electron temperature while the interband component decreases. Moreover, our model compares well with density functional theory-based calculations for the reflectivity of highly excited gold and reproduces many of its key features. Applying our methods to thin films shows a sensitive nonlinear dependence of the reflection and absorption on the electron temperature. These features are more prominent at small photon energies and can be highlighted with polarized light. Our findings offer valuable insights for modeling ultrafast processes, in particular, the pathways of energy deposition in laser-excited samples.