Surface plasmon resonance dynamics in silver nanoparticles

Summary form only given.The possibility of optically creating and probing a nonequilibrium transient electron population with femtosecond pulses has been recently applied to the investigation of electron dynamics in metal nanoparticles. Apart from alteration of the electron scattering processes by confinement, the transient response of metal nanoparticles is modified by the surface plasmon resonance consequence of the dielectric confinement. In a classical description, this corresponds to a collective oscillation of the electrons in a nanoparticle, and an important aspect in this case is the coupling between this collective motion and the individual motion of the electrons. We investigated this process and the effect of the noninstantaneous electron gas thermalization on the surface plasmon resonance properties using a two-color pump-probe technique in the low perturbation regime. We show that, in contrast to the previous measurements in copper and gold systems that have shown a response dominated by the resonance broadening, modification of the free electron distribution in silver leads to both a red shift and a broadening of the surface plasmon resonance.