<title>Influence of surface roughness on frequency shift and third-order nonlinear susceptibility of adsorbed particles</title>

Abstract

In this work we present experimental data that show that the roughness of a metal surface strongly influences the metal induced optical transition frequency shift of alkali atoms that are adsorbed close (a few tens of Angstroms) to the metal. The metal induced changes of electronic lifetime depend on distance d4, suggesting surface electron hole pair excitation to be the dominant relaxation mechanism for electronically excited Na atoms at distances between 24 and 32 A from a rough Au surface. The nonlinear response of metal surfaces is also well known to be enhanced by surface roughness. It has been anticipated that this enhancement should be most pronounced for a third order nonlinear optical process. Here, we present data of strong enhancement of x1 for rough metal surfaces. The surfaces consist of large alkali metal clusters, adsorbed on dielectrics. By changing the cluster size distribution we are able to study the third order nonlinearity as a function of shape of the alkali protrusions.