Origin of the Norton-type wave scattered by a sub-wavelength metallic slit

Abstract

We analytically and numerically clarify the physical origin and the behaviour of the Norton-wave scattered by a narrow slit, at optical frequencies. This apparently surface field, which comes in addition to the surface plasmon polariton and classical cylindrical lightwaves, features its own scattering lobe associated to oscillating induced currents extending within both horizontal metal parts forming the slit. Theory is given taking into account the finite size of the aperture.