Size dependent optical second harmonic generation from surface bound Na clusters: comparison between experiment and theory

Abstract

Optical second harmonic (SH) generation from large Na clusters bound to dielectric surfaces is reported for laser excitation with λ = 660 nm. A pronounced maximum of SH yield is found as a function of increasing (via growth) and decreasing (via thermal desorption) cluster size, which results from SH enhancement by collective surface plasmon excitation. Experimental measurements, performed both at λ = 660 nm and λ = 1064 nm are found to be in good agreement with predictions derived from the electromagnetic field enhancement theory, thereby suggesting that χ (2) for large Na aggregates is independent of cluster size. The observation of SH as a function of surface temperature shows that thermal desorption results in a strongly changing size distribution for clusters remaining on the surface that differs significantly from the distribution imposed by adsorption processes.