Surface optical second harmonic generation from rutile TiO2(110) in air

We have measured the azimuthal angle dependence of the SH intensity from the (110) face of TiO2 (rutile) in air at the fundamental photon energy of 2.33 eV. The pattern of the SH intensity shows two-fold symmetry for the p-in/p-out polarization configuration, four-fold symmetry for the p-in/s-out polarization configuration, and two-fold symmetry for the s-in/p-out polarization configuration. From the results of the experimental and theoretical analyses we have concluded that the observed SH light is generated from the surface electric dipole polarization.