NEAR-FIELD OPTICAL IMAGING USING METAL TIPS ILLUMINATED BY HIGHER-ORDER HERMITE-GAUSSIAN BEAMS

We propose a new scheme for high-resolution near-field optical imaging . The method relies on the highly enhanced fields at sharp metal tips under laser illumination. These fields are laterally confined to the t ip size and can be used to locally excite the sample surface. Illumina tion along the tip axis with a higher-order beam mode (Hermite-Gaussia n(1,0) mode) and detection of nonlinear responses (two-photon fluoresc ence, generation of second/third harmonics) ensure sufficient backgrou nd discrimination. We outline the theory of laser beams beyond the par axial approximation and investigate the electromagnetic fields for the proposed scheme. (C) 1998 Elsevier Science B.V. All rights reserved.