Field enhancement of nano-sized metal aperture with and without surrounding corrugations through resonant surface plasmons

The different behaviors of the surface plasmons along the in-plane surface of silver sheet and along the side wall of bare aperture inside the same sheet are analyzed, and their respect roles to the final field enhancement are discussed as well. The short pitch surface plasmons resonance along the side wall of the aperture is regarded as the origin of the thickness dependence of the field enhancement at the exit side of the aperture. Several solutions such as corrugation incident plane, protrusion design at the exit side to realize maximized field enhancement at the exit side of aperture are proposed. Furthermore, the step and non-step nano-sized silver apertures surrounded with circular surface corrugation structures were compared in detail. It was proved that if the 40 run sized step aperture with circular grating the near-field intensity can reach up to around 1000 times enhancement factor at the immediate exit and around 400 times enhancement even if at the plane of 10 nm away from exit of aperture.