Dispersion measurements of second-harmonic generation from a clean Cu(111) surface show a resonance feature at the second-harmonic (SH) photon energy of 4.1 eV, consistent with an image-potential-state to surface-state transition in agreement with polarization selection rules. The sensitivity of the SH efficiency to surface defects on Cu(111), observed by Bloch et al. [Phys. Rev. B 45, 12 011 (1992)], is explained in terms of an inherent energy broadening of the surface-state wave function.

• Received 10 November 1993

DOI:https://doi.org/10.1103/PhysRevB.49.17303