Second-harmonic generation from individual surface defects under local excitation

Enhancement of optical second-harmonic generation (SHG) at individual defects on metal surface has been studied. SHG has been excited locally at chosen defects using a near-field optical microscope with an uncoated fiber tip. SH intensity enhancement up to ten times has been observed at the apex of micron size defects on a gold surface while the average enhancement is of about 1.2 times. Observed SHG enhancement has been described by lightning rod effect. Specific features of SHG enhancement due to local excitation are briefly discussed.