THEORY OF OPTICAL-2ND-HARMONIC GENERATION FROM STEPPED METAL-SURFACES

The nonlinear optical response of regularly stepped (vicinal) jellium surfaces is calculated with the aim of obtaining a microscopic understanding of the isotropic and anisotropic contributions to the second-harmonic surface polarization. The ground-state electronic properties are determined self-consistently using the local-density-functional scheme and the nonlocal dynamical response to the applied laser field is treated within the time-dependent local-density-approximation approach. Although the screening effects are not yet completely taken into consideration in the present work, these calculations provide detailed information on various important aspects of the induced harmonic surface currents: their perpendicular and parallel spatial distribution, their relative magnitudes and phases, and their variation with frequency and with step density. The overall size of the anisotropic polarization terms is found to be much smaller than the leading isotropic contribution due to the normal response of the terraces. These results differ from recent experiments of second-harmonic generation from stepped Al surfaces which suggest, at 1.5 eV fundamental frequency, isotropic and anisotropic surface polarization sources of comparable magnitude.