Effect of a nonthermal electron distribution on the electron-phonon energy relaxation process in noble metals.

Abstract

We show experimentally that the electron distribution of a laser-heated metal is a InonthermalR distribution on the time scale of the electron-phonon (e-ph) energy relaxation time ${\mathrm{\ensuremath{\tau}}}_{\mathit{E}}$. We measured ${\mathrm{\ensuremath{\tau}}}_{\mathit{E}}$ in Ag and Au films as a function of lattice temperature (10--300 K) and laser-energy density (0.3--1.3 J ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$), combining femtosecond optical transient-reflection techniques with the surface-plasmon polariton resonance. Calculations support the experimental result that the nonthermal distribution leads to a IslowerR e-ph energy relaxation process below room temperature, compared to the thermalized limit.