Strong localization of near-field second-harmonic generation for nonlinear mesoscopic surface structures

The combination of scanning near-field optical microscopy (SNOM) and second-harmonic generation (SHG) spectroscopy provides a superior way, sensitive on an atomic scale, to analyze surface structures in a subwavelength resolution. We apply the self-consistent integral equation formalism to investigate the optical near field of SHG for mesoscopic nonlinear surface structures excited by a total internal-reflection beam. SHG near field is shown to strongly depend on the polarization state of excitation light. However, in various polarization states, they all exhibit a much stronger lateral localization effect than fundamental wave. This contrast can be attributed to the different interference features of elementary and secondary near field for fundamental and second-harmonic waves. Such a strong three-dimensional localization effect of SHG near field is of much convenience to an experimental observation of mesoscopic surface structures with use of SNOM. [S0163-1829(99)02419-4].