Evanescent coupling of transmitted light through an array of holes in a metallic film assisted by transverse surface current

The ultraordinary transmission of light through an array of holes in both perfect and real metallic films is simulated with the three-dimensional finite-difference time-domain method. We demonstrate that two distinguishing physical processes dominate the transmission behaviour: transverse surface current excited on the entrance surface of the metallic film transports light energy to the holes, while the evanescent coupling of incident and reflected waves inside the holes transmits light from the entrance to the exit of the holes. Surface plasmons excited on the flat parts of metallic hole arrays make a positive impact in the energy transportation of the first process, but are not necessary for the enhanced transmission. Our results are contrary to some recent theoretical results but agree with the experimental observations available.