Ultrafast electron dynamics and optical nonlinearities in metal nanoparticles

The femtosecond optical response of noble metal nanoparticles and its conne ction to the ultrafast electron dynamics are discussed in light of the resu lts of high-sensitivity femtosecond pump-probe experiments. The physical or igins of the nonlinear responses in the vicinity of the surface plasmon res onance and interband transition threshold are analyzed using extension of t he theoretical models used in the bulk materials. These responses contain i nformation on the electron interaction processes (electron-electron and ele ctron-phonon scattering) that can thus be directly investigated in the time domain. Their size and environment dependences are discussed, and the resu lts are compared to the ones in the bulk materials. Time-resolved technique s also permit direct study of the vibrational modes of metal nanoparticles and, in particular, the determination of their damping, which is a sensitiv e probe of the nature of the surrounding matrix and of the interface qualit y.