Chapter 8 - Apertureless near-field microscopy of second-harmonic generation

Abstract

The chapter discusses apertureless near-field microscopy of second-harmonic generation (SHG). Optical SHG is a nonlinear process leading to a partial transformation of the incident electromagnetic field at frequency in the second-harmonic field at the frequency after interaction with a material system. The generation of the second-harmonic signal in the aperture-less SHG SNOM can be considered taking into account the electromagnetic coupling between the surface and the probe tip at both fundamental and second-harmonic frequencies. The electromagnetic interaction between the tip and the surface results in the establishment of a local field at the fundamental frequency. This local field generates the second-harmonic field because of the second-order nonlinear susceptibility of the surface and/or the tip. The SH signal reveals distinct resonant behavior related to the excitation of localized surface plasmon in the system of coupled spheres used as the tip and defect in model calculations. The intensity of the far- and near-field scattering from a tip apex follows polarization dependence. The measured polarization dependencies of the scattering from the tip under the near- and far-field excitation are in good agreement with the model for all measured tips.