Multipole analysis of the radiation from near-field optical probes

Abstract

We experimentally and theoretically analyze the radiation emitted from subwavelength-sized apertures in nearfield optical probes. By decomposing the experimentally obtained radiation patterns into vector spherical waves, we describe the fields in terms of a series of multipole sources. We fit polarization-resolved angular intensity distributions, measured as far as 150 degrees from the normal, with dipole, quadrupole, and octupole radiation. We find that the magnetic and the electric dipole components are dominant but that the interference terms between dipoles and higher-order poles are not negligible. This result can be used as the basis for understanding near-field optical interactions and images. (C) 2000 Optical Society of America. OCIS codes: 260.1960, 180.5810.