Control of the tip–surface distance in near-field optical microscopy

Abstract

An experimental technique that makes use of the intensity of the interference pattern formed by light that propagates directly from the single-mode fiber tip and light that is reflected by the surface under an oblique angle of incidence is developed to control the tip–surface distance in near-field optical microscopy. It is shown that by using another fiber as a detector with a polished edge placed at the surface near the fiber tip one can determine the tip–surface separation with an accuracy better than 15 nm at distances less than 1 μm. The technique proposed is used to investigate the influence of the shape of the tip in near-field measurements.