Theoretical analysis of scanning near‐field optical microscopy

Abstract

The near‐field optical (NFO) interaction between a pointed detector and dielectric or metallic substrates can be exploited to perform both nanometer scale topographies or spectroscopies of surfaces in the real space. The correlation of optical signals recorded with such detectors with other properties of the object (shape, index variation, … ) provides a wealth of new opportunities for characterization of small objects which has not yet been completely assessed. In fact, this new field represents a challenge to theoretical optics since NFO effects often are beyond the scope of classical theories. We present in this contribution a detailed study of both tip‐sample interactions and optical energy transfer occurring in scanning near‐field optical microscopy (SNOM). The treatment is based on the field‐susceptibility method applied in the real space. In this description, all multiple interactions including reflections with a substrate of arbitrary profile are accounted for by the usual self‐consistent equations. An original numerical scheme, based on a discretization procedure in the real space, is used to compute the field inside SNOM devices. This contribution reports the results of the numerical applications of this method to various NFO effects including, image‐object relation, nearfield spectroscopy of metallic aggregates, light‐induced forces, and nonlinear effects in confined geometry. Copyright © 1994 Wiley Periodicals, Inc.