Second-harmonic scanning optical microscopy of individual nanostructures

Second-harmonic far- and near-field optical microscopy of individual subwavelength-sized objects placed on a substrate surface is considered by making use of a macroscopic self-consistent approach for second-harmonic microscopy extended to take into account the presence of a (linear or nonlinear) substrate. Second-harmonic optical images in the illumination configuration are calculated for the cases with a scanning Gaussian beam and with a scanning probe being the source of illumination. Object-substrate combinations with various nonlinear properties are considered for different polarization configurations of illuminating and detected radiation. We show that the symmetry of second-harmonic images is strongly influenced by the nonlinear properties of the object and substrate. The results obtained are discussed and related to the available experimental images.