Femtosecond decay-time measurement of electron-plasma oscillation in nanolithographically designed silver particles

The decay time of the electron-plasma oscillation in silver nanoparticles is measured at a nanoparticle film consisting of regularly arranged. identically shaped and identically oriented particles. By design of a noncentrosymmetric particle shape, SHG in transmission at normal incidence oft he fundamental beam is obtained. Therefore the autocorrelation function of the optical near field oscillation of the particle, excited by two temporally overlapping fs laser pulses separated by a defined delay time, could be measured. A decay time of 10+/-1 fs was extracted. This result shows that the damping of the electron-plasma oscillation in nanometric particles is approximately a factor of 2 larger than expected from the value of the imaginary part of the bulk metal dielectric function when consideration of the radiation damping in the particles is included.