Observation of Rotational Anisotropy in the Second-Harmonic Generation From a Metal Surface.

We show that crystalline metal surfaces, in particular the Cu(111) surface, exhibit strong SH rotational anisotropy. The form of this anisotropy is fully predicted by the current theory of SH from the surface and near-surface bulk of centrosymmetric media. This SH anisotropy allows measurements of changes in atomic order, eg. phase transitions, on metal surfaces. Since the anisotropic contribution can only arise from interband transitions, it provides greater SH sensitivity to distinguishing adsorbate binding sites.