Optical second harmonic spectroscopy of the Au(100) 5x20 reconstructed surface

We have performed SH spectroscopy on a reconstructed Au(100) 5 x 20 surface. We have found a broad SH intensity continuum for the SH photon energy from 2ħω = 2.2 to 4.2eV. Between the photon energies 2ħω = 3.7 and 4.2eV, the SH intensity in the s-in/p-out (s-polarized input and p-polarized output) polarization configuration is stronger than that in p-in/p-out polarization configuration, but the former signal disappeared when the surface was exposed to air. Surface electronic states are suggested to contribute to the SH response in this photon energy region