Size-Dependent Plasmon Lifetimes and Electron-Phonon Coupling Time Constants for Surface Bound Na Clusters

In this paper we show that time-resolved analysis of second harmonic generation via femtosecond pump-probe studies can be used to extract simultaneously mean cluster radii, decay times τₛₚ of localized surface plasmon excitations, and electron-phonon coupling time constants τₑₚ in large Naₙ (n≈10⁷) clusters, bound to insulator surfaces. From the dependence of plasmon lifetime on the mean cluster radius (5≤r₀≤55nm) a maximum of τₛₚ0ex0ex=0ex0ex10fs at a mean radius of about 25 nm is observed. Additionally, for Na clusters with mean radii of 30 to 50 nm and bound to a lithium fluoride surface the electron-phonon coupling time constant is found to be τₑₚ≈1.1ps.