Inspection of nano-sized SNOM-tips by optical far-field evaluation

High resolution optical microscopy has many interesting applications in sol id state physics. low temperature physics, biology and semiconductor techno logy. Unfortunately, the lateral resolution of conventional microscopes is limited by the Rayleigh-limit. "Scanning nearfield optical microscopy" (SNO M) seems to be a promising new approach to characterize the properties of m aterials optically with a high lateral resolution of 50 100nm. The most imp ortant part of such a microscope is the scanning probe (a special glass fib er tip). However, the quality of the optical fiber tip is of decisive impor tance. Since the production process of pulled and coated glass fiber tips i s still highly empirical and error-prone, a technique would be useful to de termine the tips' quality before they are shipped to the user or mounted in the microscope. The tips' apertures are smaller than lambda /2 and therefo re they cannot be measured in a non-destructive way by conventional optical microscopy. This paper discusses an easy and fast method for the optical c haracterization of common glass fiber SNOM tips. The effective aperture of the tip is measured from the far-field distribution of the emitted intensit y recorded by a CCD target. A numerical model is introduced to solve this i nverse task and a simple optical setup is presented to detect light emitted by the tip at an angle of up to 90 degrees from the optical axis. Experime ntal investigation, near/far-field calculations and scanning electron micro scope investigations show the working principle of this measurement techniq ue for the analysis and evaluation of a typical nanostructured object. (C) 2001 Elsevier Science Ltd. All rights reserved.