Materials structured on the nanometer scale can lead to improved and sometimes surprising properties. This will be illustrated in some detail by our own work on the extraordinary optical properties acquired by metal films when their surfaces are corrugated and perforated with one or more sub-wavelength holes (~150 nm). Such structures can transmit the light with an efficiency hundred times larger than what theory predicts for single holes. The efficiency can even be much
larger than the fractional area occupied by the hole, which means that even the light falling beside the hole emerges on the other side of the sample. This extraordinary transmission is due to the coupling of the incident light with the surface plasmons of the film. The transmission spectrum contains peaks attributed to surface-plasmon modes that depend on both the symmetry and the 2D lattice parameter of the surface corrugation. Novel results show that an other fundamental problem
of sub-wavelength apertures, namely optical diffraction, can also be modified using surface plasmons. The optical divergence and directionality of light transmitted by a single subwavelength aperture can be controlled. These results have broad fundamental and practical implications and show that, with modern fabrication techniques, surface plasmons can be engineered to yield unique optical properties.

References: Ebbesen et al Nature 391, 667 (1998); Ghaemi et al, Phys. Rev. B 58, 6779 (1998); Grupp et al Adv. Mater. 11, 860 (1999); Kim et al, Optics Letters 24, 256 (1999); Grupp et al, Appl. Phys. Lett., 77, 1569 (2000); Martin-Moreno et al, Phys. Rev. Let.. 86, 1114 (2001); Krishnan et al. Optics Comm. 200,
1 (2001); Lezec et al Science, in press (2002).