Observations of second-harmonic generation from randomly rough metal surfaces

The angular distributions of second-harmonic light scattered from metal surfaces with weak random roughness are studied experimentally. The power spectrum of the roughness has a rectangular form centered on the surface plasmon polariton wave number at the fundamental frequency, producing strong excitation of these surface waves. The scattering distributions exhibit a pair of distinct peaks at angles consistent with the nonlinear interaction of the incident wave with fundamental plasmon polaritons. The controlled experiments allow a number of other scattering processes to be identified that include, for example, the nonlinear excitation of surface plasmon polaritons at the harmonic frequency. A peak in the second-harmonic distribution, predicted to appear in a direction perpendicular to the mean surface, is not observed.