Near-field second-harmonic generation at a metal tip apex

Second-harmonic generation at a gold tip apex has been studied within the context of applications in apertureless scanning near-field microscopy. Polarization and distance dependencies of second-harmonic generation have been investigated and compared to respective dependencies for scattered fundamental light. The results shows that, in general, different topological features of a tip are responsible for scattering and second-harmonic generation in the far and near field. The near-field interaction between a probe tip and a surface significantly modifies enhancement of the electromagnetic field at the tip and results in different distance dependencies of near-field scattering and second-harmonic generation. The polarization contrast obtained with the second-harmonic signal significantly exceeds the polarization contrast of linear scattering from the tip. (C) 2002 American Institute of Physics.