SURFACE ELECTROMAGNETIC-WAVES IN NEAR-FIELD OPTICAL-SCANNING MICROSCOPY

Because their electromagnetic fields are localized to the surfaces tha t support them, surface electromagnetic waves are more sensitive to ge ometrical and dielectric perturbations in their propagation path than are volume electromagnetic waves incident on the same surface perturba tions. This suggests that a near-field optical microscopy based on sur face electromagnetic waves could reconstruct surface profiles with gre ater resolution than one based on the scattering of volume electromagn etic waves from surfaces with the same profiles. In this work we study the scattering of a surface plasmon polariton propagating along a met al surface and incident normally on an isolated surface defect. We cal culate the intensity of the total field at constant height from the un perturbed surface to first order in the surface profile function. The result can be written in terms of the convolution of the surface profi le function and a function that depends only on the properties of the metal surface. We invert this result by a Fourier transform method to obtain the surface profile function. As experimental data we use the r esults of a rigorous numerical solution of the corresponding reduced R ayleigh equation. Structures on the surface with lateral dimensions of the order of one-tenth the wavelength of the incident surface polarit on have been reconstructed in this way. (C) 1998 Elsevier Science B.V. All rights reserved.