Size-dependent dynamical screening effects in metal nanoparticles: ultra-fast pump-probe signal

Summary form only given. The absorption of light by metal nanoparticles is dominated by the surface plasmon (SP) resonance. Although the linear absorption spectrum has been extensively studied, little is known about the SP nonlinear optical dynamics. The electron relaxation in Cu nanoparticles was recently studied with femtosecond pump-probe spectroscopy. During the thermalization that follows the heating of the electron gas by the pump pulse, the relaxation was observed to exhibits a strong frequency dependence near the SP resonance. We address the role of collective surface excitations in the electron relaxation in metal nanoparticles. We demonstrate that e-e interactions inside small particles are strongly modified by a surface-induced dynamical screening. This leads to a quasiparticle scattering accompanied by the emission of SPs.