Electron-electron and electron-lattice interactions in noble metals are discussed in the light of two-color femtosecond pump-probe measurements in silver films. The internal thermalization of a nonequilibrium electron distribution created by intraband absorption of a pump pulse is followed by probing the induced optical property changes in the vicinity of the frequency threshold for the d band to Fermi surface transitions. This is shown to take place with a characteristic time constant of 350 fs, significantly shorter than previously reported in gold. This difference is ascribed to a weaker screening of the electron-electron interaction by the d-band electrons in silver than in gold. These results are in quantitative agreement with numerical simulations of the electron relaxation dynamics using a reduced static screening of the electron-electron Coulomb interaction, and including bound electron screening. Electron-lattice thermalization has been studied using a probe frequency out of resonance with the interband transitions. In both materials, the transient nonthermal nature of the electron distribution leads to the observation of a short-time delay reduction of the energy-loss rate of the electron gas to the lattice, in very good agreement with our theoretical model.

International audienceElectron-lattice energy exchanges are investigated in gold and silver nanoparticles with sizes ranging from 30 to 2.2 nm embedded in different environments. Femtosecond pump-probe experiments performed in the low-perturbation regime demonstrate a strong increase of the intrinsic electron-phonon interaction for nanoparticles smaller than 10 nm due to a confinement effect