Femtosecond surface plasmon resonance dynamics and electron-electron interactions in silver nanoparticles

Femtosecond excitation and relaxation of nonequilibrium electrons are inves tigated in silver clusters using a two color pump-probe technique with reso nant excitation of the surface plasmon resonance and off resonant probing. The excitation process is shown to be identical to that in metal films, and permits creation of a strongly athermal single electron excitation in a ti me scale shorter than the duration of the pulses (25-30 fs), in agreement w ith the free-electron absorption model. Following the time evolution of the nonequilibrium distribution yields information on the internal energy redi stribution dynamics of the conduction electrons and of its modification by confinement in metal clusters.