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The resolution of near-field optical scanning microscopy (NFOS) is determined by the dimensions of the microscopic light source rather than the diffraction limit. To demonstrate NFOS in reflection, intensity changes in the (backward) scattering from a 70–100 nm diam hole in a metal film were recorded while the sample was scanned in close proximity to this aperture. Raster-scan images of a planar metal test pattern yield a resolution comparable to the size of the aperture.
Fischer et al. (1988) studied this question.