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 light guided in a metal-clad tapered optical fiber. We investigate different orientations of the aperture in the plane: normal to the cleaved plane, oblique to the cleaved plane, and off-center. We measure the far-field, two-dimensional intensity distributions of the diffracted light as functions of angle coordinates theta and phi in a full half-space for various polarization states and analyze the patterns by using low-order multipole fields. We also examine the near- and far-field effects of placing small periodic corrugations near the aperture, focusing on the role of surface-wave excitations. 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.