Pump-probe spectroscopy study of ultrafast temperature dynamics in nanoporous gold

Abstract

We explore the influence of the nanoporous structure on the thermal relaxation of electrons and holes excited by ultrashort laser pulses ($\ensuremath{\sim}7\phantom{\rule{0.16em}{0ex}}\mathrm{fs}$) in thin gold films. Plasmon decay into hot electron-hole pairs results in the generation of a Fermi-Dirac distribution thermalized at a temperature ${T}_{\mathrm{e}}$ higher than the lattice temperature ${T}_{\mathrm{l}}$. The relaxation times of the energy exchange between electrons and lattice, here measured by pump-probe spectroscopy, is slowed down by the nanoporous structure, resulting in much higher peak ${T}_{\mathrm{e}}$ than for bulk gold films. The electron-phonon coupling constant and the Debye temperature are found to scale with the metal filling factor $f$ and a two-temperature model reproduces the data. The results open the way for electron temperature control in metals by engineering of the nanoporous geometry.