Femtosecond response of a single metal nanoparticle.

The ultrafast nonlinear optical response of a single metal nanoparticle is investigated by combining a high-sensitivity femtosecond pump-probe setup with a spatial modulation microscope. Experiments are performed on 20 and 30 nm silver nanospheres, in situ characterized via their optical linear extinction spectrum. The measured transient response permits investigation of the electron-phonon energy transfer time in a single nanoparticle. Its dependence on the electronic temperature is quantitatively interpreted using the two-temperature model.