2ND-HARMONIC GENERATION FROM METAL-SURFACES - BEYOND JELLIUM

The generation of Second-Harmonic (SK) radiation from simple metals ha s been the subject of numerous investigations for almost three decades . The use of clean metal surfaces in the experiments and increasingly sophisticated jellium-based theoretical models has led to a convergenc e on the magnitude and some of the dispersion characteristics of SH ge neration in free-electron metals like aluminum. However, the sensitivi ty of the SH-generation process to crystal symmetry, surface morpholog y, and surface electronic states indicates that nonlinear optical prop erties are influenced by processes which cannot be explained using a m odel based on an isotropic electron gas. Here, we review some recent e xperimental work indicating where deviation from jellium-based models occurs and attempts to understand these.