Light diffraction by a subwavelength circular aperture

Diffraction of normally incident light by a subwavelength circular aperture is calculated analytically. The aperture is opened on a perfectly conducting planar screen with infinitesimal thickness. In our model, the aperture is replaced by uniform magnetic currents and charge. The model allows one to obtain the normalized cross section for the aperture radius up to half of the wavelength, which exceeds the 0.2 wavelength limit of the Bethe-Bouwkamp's dipole model [1-3]. Also, in addition to reproducing the (ka)(4) dependence, which is characteristic of the dipole mode, our uniform field model explains the transmission enhancement obtained in Abajo's numerical simulation [4].