Transmission Enhancement in an Array of Subwavelength Slits in Aluminum Due to Surface Plasmon

The coupling of light to surface plasmons through periodic subwavelength metallic structures could strongly modify the optical properties of a metal film. We demonstrate that the optical transmission through an array of subwavelength slits is as high as 80 % at resonance, even though the width of each slit is almost 10 times smaller than the wavelength and the slits occupy only 25 % of the area of the metal. Numerical calculations suggest that the field intensity is strongly enhanced near the metal surface. The field enhancement could be used for generating nonlinear optical effects and for high sensitivity detection of nanomechanical displacement. © 2005 Lucent Technologies Inc. Surface Plasmons on a Metallic Surface Surface plasmons are collective excitations of the electron density guided by a metal-dielectric interface [23]. They are solutions to Maxwell’s equations in which the charge oscillations are localized at the metal boundary (see Figure 1). The charge oscillation takes place in the longitudinal (x) direction parallel to the wavevector, as shown in Figure 1a. The charge den-sity fluctuation is associated with an electromagnetic field that is maximum at the surface and decays ex-ponentially away from it. On a smooth metal sur-face, the dispersion relation for surface plasmons is given by (1) where e1 and e2 are the dielectric functions of the metal and the dielectric, respectively. Figure 1b is a k v c a e1e2 e1 e2 b12