Apertureless near-field optical microscopy via local second-harmonic generation

We describe an apertureless scanning near-field optical microscope (SNOM) b ased on the local second-harmonic generation enhancement resulting from an electromagnetic interaction between a probe tip and a surface. The imaging mechanisms of such apertureless second-harmonic SNOM are numerically studie d. The technique allows one to achieve strongly confined sources of second- harmonic light at the probe tip apex and/or surface area under the tip. Fir st experimental realization of this technique has been carried out using a silver-coated fibre tip as a probe. The experiments reveal a strong influen ce of the tip-surface interaction as well as polarization of the excitation light on images obtained with apertureless second-harmonic SNOM. The techn ique can be useful for studying the localized electromagnetic excitations o n surfaces as well as for visualization of lateral variations of linear and nonlinear optical properties of surfaces.