Abstract: New experimental technique for near-field observation of second-harmonic generation is discussed. This technique gives the unique possibility for the investigation of local optical nonlinear processes with subwavelength resolution and will be useful for the characterization of materials as well as for fabrication and utilization of optical nonlinear devices at nanometer scale. Peculiarities of optical nonlinear processes in near-field region have been studied. The difference in the mechanisms of second-harmonic generation for different polarizations of excitation light has been demonstrated for rough metal surfaces. The dependence of second-harmonic intensity on tip-surface distance has been examined verifying the presence of strong evanescent SH field components. The technique has been applied for characterization of optical nonlinear crystals (LiNbO$-3$/ and KDP), ferromagnetic and ferroelectric materials. The spatial resolution of the microscope in the SH light collection mode has been determined to be better than 150 nm. !27
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