Ultrafast relaxation dynamics of electronic excitations in noble-metal clusters

We investigate non-equilibrium relaxation processes in optically excited la rge gold and silver clusters. Time-resolved pump-probe experiments and mode l calculations show that optical excitation of the clusters by femtosecond laser pulses results in a heating of the electron system, which is followed by electron cooling via phonon emission. The electron heating leads to an enhanced damping of the surface-plasmon resonance in the clusters. This enh anced damping is caused by an enhancement of the Landau damping and electro n scattering rates at high electron temperatures. Furthermore, we find that the rate of electron cooling in the clusters changes with electron tempera ture; this is a consequence of the temperature-dependent specific heat of t he conduction electrons. Finally, pump-probe experiments on ellipsoidal sil ver clusters show that the thermal expansion of the heated clusters trigger s mechanical vibrations at the acoustic eigenfrequencies of the clusters.