Surface-dipole and electric-quadrupole contributions to anisotropic second-harmonic generation from noble-metal surfaces

The azimuthal anisotropy in the optical second-harmonic response from various crystal faces of Ag, Cu, and Au has been measured. Comparing the relative magnitude of the isotropic and anisotropic signals indicates that the strong anisotropy observed from the (111) and (110) faces of noble metals can be assigned primarily to the dipolar surface response. This result contrasts to the case of Al single crystals where the anisotropy can be accounted for by the bulk quadrupole response.