Resonant surface second-harmonic generation on Cu(111) by a surface state to image-potential state transition

The authors present the first observations of resonant enhancement of χ⁽²⁾ from a metal by a surface state-image potential state transition. This conclusion is reached from a systematic experimental investigation of second-harmonic (SH) generation from a clean Cu(111) surface as a function of photon energy, and crystal azimuthal orientation. The authors also suggest that earlier observations of the sensitivity of the SH resonance in Cu(111) to lattice temperature and bombardment of the surface by ions can be explained by a linewidth broadening associated with electrons in surface states scattering into bulk states, consistent with angle-resolved photoemission measurements