Two resonances effect for light transmission assisted with surface plasmon through perforated metal film

When light is incident on a nonplanar metal surface, an oscillating dipole is excited at the entrance openings. We show that the enhanced transmission assisted with surface plasmon (SP) through a perforated metal film results from two different SP resonances effects: (i) zero-order Fabry-Perot resonance effect where each air hole can be considered as a section of metallic waveguide, forming a low-quality-factor resonator, and many dipoles are arranged inside the nanoholes region; and (ii) structure-factor-induced charges self-tunnelling effect due to the well-recognized surface structure periodicity, where the positive or negative charges can respectively tunnel into the right surface through the metal walls. Furthermore, when light transmits through the double-layer perforated metal films, the different transport behaviors are also clearly shown, which convinces the existence of dual SP resonances effect.