Near-field second harmonic generation from a rough metal surface

Local second-harmonic generation (SHG) from a rough metal surface has been measured using a near-field optical microscope. The dependence of the SH signal on the tip-surface distance for excitation with $S$- and $P$-polarized light shows the presence of evanescent SH field components. With excitation by $S$-polarized light the SHG over the rough surface is found to be strongly related to surface topography. For $P$-polarized light excitation, local enhancement of SH emission have been observed that may be attributed to SH field localization.