NONGLOBAL MODEL FOR A NEAR-FIELD SCANNING OPTICAL MICROSCOPE USING DIFFRACTION OF THE OPTICAL NEAR-FIELD

Diffraction of the localized optical near field by a subwavelength-siz ed probe (metallic circular aperture) is studied by a nonglobal approa ch. The problem is closely relevant to the basic principle of a near-f ield scanning optical microscope (NSOM). We obtain analytic expression s of the diffracted far field from which the transfer function of the NSOM can be calculated. In particular, we find a resonance enhancement in the detection efficiency when the sample size is similar to the pr obe size. By lateral scanning of the aperture position at a constant h eight, we also obtain a NSOM image of a dielectric sphere sample. (C) 1996 Optical Society of America