Bouhelier, Alexandre; Beversluis, M.; Hartschuh, Achim; Novotny, Lukas
Near-Field Second-Harmonic Generation Induced by Local Field Enhancement.
In: Physical Review Letters, Vol. 90, No. 1: 013903-1-013903-4
The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes.