Intermediate field behind a nanostructure

Abstract

The field behind a subwavelength nanohole in a perfectly conducting plate is considered as an idealization of photonic nanostructures. It is stressed that even with nanophotonic or plasmonic structures, the fields in the neighboring free space must satisfy classical electrodynamics. We present scalar and electromagnetic treatments for the fields behind a small hole in a thin, perfectly conducting screen, and give an expression for the total field along the complete axis behind the hole, from near field to far field. Bouwkamp corrected Bethe's expression for the electric field behind the hole. We show that Bouwkamp's solution for the magnetic field needs two additional terms in order for the total field to be given satisfactorily by the sum of the evanescent field and the homogeneous field of a magnetic dipole. The fields are separated into near-field and far-field components, avoiding oscillations caused by interference between them. The variation of the Poynting vector is also considered.