We report the first direct measurement of the relaxation of plasma oscillations in a solid. Via the second-harmonic autocorrelation of femtosecond laser pulses, the lifetimes of localized plasma oscillations in silver island films were investigated. Decay times of 40±7 fs were obtained, which indicate that single-particle scattering is mainly responsible for the energy relaxation of the plasma oscillations.

• Received 9 September 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.389