Resonance absorption of metallic plate with subwavelength hole array

The optical reflectance by a metallic plate arranged with array consisting of subwavelength periodic square hole is investigated by using the three-dimensional finite-difference time-domain method (3D-FDTD). There are dips in the reflectivity spectra, which indicate the absorption peaks. The absorption peaks behave differently according to the ratio of hole width and the period of the hole array. Combined with the near fields of the absorption peaks, it is found that the surface plasmon (SP) resonance on the surface of plate and localized SP in the hole play a major role for the two absorptions.