Electron thermalization in gold

The direct observation of the thermalization of electrons in Au following 180 fs optical pulse excitation is reported. The evolution of the electron energy distribution from the nascent (as photoexcited) to a hot Fermi--Dirac distribution was measured by time-resolved photoemission spectroscopy. Depending on the excitation density, thermalization times as long as approx 1 ps were observed. A model incorporating both electron--electron and electron--phonon scattering, and using Fermi-liquid theory to properly account for screening is found to reproduce the main features of the experiment.