Ultrafast optical relaxation dynamics in metallic nanoparticles: from bulk-like toward spatial confinement regime Original Research Article

A detailed analysis of the ultrafast optical response of gallium and tin clusters, embedded in a dielectric matrix, with sizes ranging from the sub-micrometer to the nanometer region is presented. Two distinct regimes of relaxation dynamics depending upon particle radius are observed. Particles with a radius greater than the mean electronic free path present similar temporal evolution of the excitation decay with superimposed damped oscillations, interpreted in terms of acoustic waves generated inside the particle. For nanoparticles with a radius smaller than the mean electronic free path, a clear size dependence of relaxation dynamics is observed. This is a strong indication of an efficient electrons–surface phonon interaction in this regime.