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 tau(sp) of localized surface plasmon excitations, and electron-phonon coupling time constants tau(ep) in large Na-n (n approximate to 10(7)) clusters, bound to insulator surfaces. From the dependence of plasmon lifetime on the mean cluster radius (5 less than or equal to r(0) less than or equal to 55 nm) a maximum of tau(sp) = 10 fs 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 tau(ep) approximate to 1.1 ps.