Ultrafast electronic dynamics in metal nanoparticles

The electronic and vibrational relaxation mechanisms of metal quantum-dots embedded in dielectric matrices following ultrashort-pulse laser excitation is a topic of intense current interest. The electronic dephasing process in metal quantum dots occurs on a time scale of 10-20 fs. The electron-phonon (e-p) coupling within the quantum dot, and the phonon-phonon (p-p) coupling between the dot and the matrix, are typically picoseconds and tens of picoseconds, respectively. Among the critical issues are variations in these time constants between intraband and interband transitions, for high vs low pulse-repetition frequency (PRF), and for different combinations of quantum dot and matrix. We have measured these time constants at high pulse repetition frequencies using both pump-probe (PP) and transient-grating (TG) schemes for well-characterized Ag, Au and Cu quantum dots of varying size distributions in fused silica. Wavelengths on and off the plasmon resonance and near as well as away from the interband excitations were employed