Alkali metal atoms, adsorbed on dielectric or semiconductor substrates, form large clusters under certain, experimentally well accessible circumstances. Both the mean radius and the size distribution of the clusters can be manipulated using appropriate values of surface temperature and deposition rate or by laser treatment. Irradiation with laser light leads to a collective electronic excitation (surface plasmon excitation), which results, via the concomitant strong electromagnetic field enhancement, in a huge enhancement of the nonlinear optical properties of the cluster films. The evolution of these properties as a function of, e.g., the cluster size can be reproduced quantitatively using classical electrodynamics.

We discuss recent findings on the second and higher order nonlinear optics from these clusters and also show for comparison results for alkali metal adsorption on semiconductors. It is demonstrated that the application of nonlinear optical methods to the cluster systems allows one to obtain real-time dynamical information on the time-constants for laser-induced desorption and for the decay of the elementary optical surface plasmon excitation into single electron excitations and finally into lattice oscillations of the clusters and the substrate. Together with a theoretical approach to the bond-breaking mechanism on the basis of multiphonon scattering theory, these results lead us to a coherent description of the dynamics of optically excited, large, surface bound alkali clusters.