Diffraction by a subwavelength-sized aperture in a metal plane

We present an experimental study on the diffraction of light by an aperture small compared with the wavelength. The aperture is illuminated by laser l ight guided in a metal-clad tapered optical fiber. We investigate different orientations of the aperture in the plane: normal to the cleaved plane, ob lique to the cleaved plane, and off-center. We measure the far-field, two-d imensional intensity distributions of the diffracted light as functions of angle coordinates theta and phi in a full half-space for various polarizati on states and analyze the patterns by using low-order multipole fields. We also examine the near- and far-field effects of placing small periodic corr ugations near the aperture, focusing on the role of surface-wave excitation s. We measure the near-field intensity distributions near the aperture with a near-field scanning optical microscope and discuss their relation to the far-field diffracted fields. (C) 2001 Optical Society of America.