Dual effect of surface plasmons in the light transmission through perforated metal films

The light transmission through perforated metal film has been studied both experimentally and theoretically. By taking account of plasma response of real metal on hole walls as well as metal surface, an analytical result for the transmission has been deduced, which agrees well with the experiments. The transmission involves both the diffraction modes and the surface plasmons. The surface plasmon polariton formed on the metal-dielectric interface gives rise to the transmission minima. Nevertheless, the cavity surface plasmons excited in the nanoholes contribute actively to the transmission enhancement. The results suggest a dual-effect of the surface plasmons. *Email: [email protected] Due to the unique dielectric response of metals, the interaction between the electromagnetic waves and artificially structured metals has been a subject of a wealth of theoretical and experimental work. For example, by using the periodic arrays of conducting wires and split-ring resonators, left-handed metamaterials have been constructed [1]. In recent years, resonant excitation of surface plasmon polariton (SPP) has sparked much attention [2]. Light that usually travels in a dielectric or vacuum is, due to coupling between light and surface charges, able to propagate along the metal surface with the amplitudes decaying into both sides. This unique feature has generated the SPP-based photonics or plasmonics. Plasmonics possessing both the capacity of photonics and miniaturization of electronics enables it to be an outstanding candidate for the future optoelectronic applications [3]. Besides the propagation of light along metal surface, the light propagation normal to the metal film is another interesting issue. When the film is optically thin (~ skin depth), the energy transfer can be enhanced by the SPP mode [4], and super-resolution imaging can be achieved [5]. And when the film thickness is much larger than the skin depth, the film will be completely opaque. However, it was found by Ebbesen et al. [6] that when subwavelength hole arrays are introduced into the metal film, a surprising effect appears. That is, the transmission of light thought to be very low can be larger