Multipole analysis of the radiation from near-field optical probes

We experimentally and theoretically analyze the radiation emitted from subw avelength-sized apertures in nearfield optical probes. By decomposing the e xperimentally obtained radiation patterns into vector spherical waves, we d escribe the fields in terms of a series of multipole sources. We fit polari zation-resolved angular intensity distributions, measured as far as 150 deg rees from the normal, with dipole, quadrupole, and octupole radiation. We f ind that the magnetic and the electric dipole components are dominant but t hat the interference terms between dipoles and higher-order poles are not n egligible. This result can be used as the basis for understanding near-fiel d optical interactions and images. (C) 2000 Optical Society of America. OCI S codes: 260.1960, 180.5810.