40 nm resolution in reflection-mode SNOM with λ = 685 nm

A reflection-mode aperture SNOM based on external collection of the reflected light is presented. The light detection is based on an elliptical mirror set-up, with the tip at one focus, and a PMT at the other. Tapered metal-coated fibres are used as SNOM probes, with a wavelength of 685 nm. Shear-force distance regulation is used. Images of a cross grating structure indicate a shear-force resolution of 20–30 nm, and an optical resolution of 40–50 nm (λ15).