Metals such as silver support surface plasmons: electromagnetic surface excitations localized near the surface that originate from the free electrons of the metal. Surface modes are also observed on highly conducting surfaces perforated by holes. We establish a close connection between the two, showing that electromagnetic waves in both materials are governed by an effective permittivity of the same plasma form. The size and spacing of holes can readily be controlled on all relevant length scales, which allows the creation of designer surface plasmons with almost arbitrary dispersion in frequency and in space, opening new vistas in surface plasmon optics.

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metaldielectric interfaces. Different regimes of tunneling (resonant through a "surface plasmon molecule", or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system. PACS numbers: 78.66. Bz, 73.20.Mf, 42.79.Dj, 71.36.+c In the last few years, and mainly due to advances in nanotechnology, there has been a renewed interest in exploiting the dielectric response of metals to make photonic materials [1][2][3]. For instance, the photonic insulating properties of metals can be used to trap incident radiation, focusing light in very small volumes [4][5][6]. Very recently [7], another interesting effect of light interacting with structured metals has been discovered: the transmission of light through subwavelength hole arrays made in a metal film can be orders of magnitude larger than expected from standard aperture theory [9]. Apart from its fundamental interest, this extraordinary transmission effect has potential applications [10,11] in subwavelength photolithography, near-field microscopy, wavelength-tunable filters, optical modulators, and flatpanel displays, amongst others. While the wavelength at which some transmission features appeared suggested [7,8] that surface plasmons (SP) [12] were involved in the process, the physical mechanism for the huge enhancement has not yet been elucidated. Some calculations have been performed for a simpler geometry: an array of slits [13][14][15], where high transmission was also predicted. However, although interesting in their own right, these results do not apply to the experimental situation.In this letter, we present the first fully threedimensional theoretical study of transmission through hole arrays, obtaining an excellent agreement with experimental data. Moreover, we develop a simplified version of the model that clearly captures the physics involved. Fig. 1 shows the experimental "zero-order" transmittance of light at normal incidence (T 00 ), through an array of holes in a free-standing metal film. The free-standing metal film, of which the fabrication is described elsewhere [8] consisted of a 220nm thick Ni core, perforated with a square array of holes by focused-ion beam milling. The film was subsequently overcoated with 50nm of Ag on both sides by sputter deposition which resulted in a coating of the walls of the holes as well as the in-plane surfaces of the film. The total thickness of the film was h = 320nm and the lattice constant of the hole array was L = 750nm. After coating the holes had an average diameter of 280nm. It has been shown [8] that such a "sandwich" structure has the same transmission properties as an eq...

We present a study on the far-field patterns of light transmitted through sub-wavelength metallic hole-arrays. Spectral imaging measurements are used here on hole arrays for the first time. It provides both spatial and spectral information of the transmission in far-field. The visibility of the images, measured in two illumination modes: Köhler and collimated, is calculated for different planes in and out of focus. The transmission under collimated illumination reveals that 75% of the beam if non-divergent. The results are in agreement with the low divergence measured by Lezec [Science 297, 820 (2002)].