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.

Electron-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.

The absorption of a single isolated metal cluster is directly measured using a novel far-field optical technique based on modulation of its position. Single gold nanoparticles with average diameters down to 5 nm, dispersed on a transparent substrate, are optically detected and their absolute absorption cross section determined.

The internal thermalization dynamics of the conduction electrons is investigated in silver nanoparticles with radius ranging from 13 to 1.6 nm using a femtosecond IR pump–UV probe absorption saturation technique. A sharp increase of the electron energy exchange rate is demonstrated for nanoparticles smaller than 5 nm. The results are consistent with electron-electron scattering acceleration due to surface induced reduction of the Coulomb interaction screening by the conduction and core electrons.