Optical diffraction of subwavelength apertures

Thomas W. Ebbesen

ISIS, Louis Pasteur University, 8 allee Gaspard Monge, 67000 Strasbourg, France

An aperture in a screen is probably the simplest optical element one could imagine and it has been an object of curiosity and technology since the Antiquity, well before it was scientifically analyzed. In the middle of the 17^th century, Grimali first described diffraction of a circular aperture contributing to the foundation of classical optics. Despite their simplicity, such apertures have remained the object of scientific studies ever since as an accurate description of their optical properties has turned out to be extremely difficult. In the 20^th century, Bethe treated the diffractive optics of subwavelength apertures in an idealized metallic screen which became the reference associated with the miniaturisation of optical elements and the development of modern characterization tools such near-field scanning optical microscopes. In the past decade new experimental results reveal that the real subwavelength apertures in metal films can have properties that are very different from the earlier theoretical predictions due to the involvement of surface plasmons in the transmission process. Most notably the transmission intensity can be much greater than Bethe’s prediction and the geometrical diffraction is far from isotropic at the exit of the aperture. This has implications in a variety of areas including the subwavelength lithographic transfer of images, near-field imaging and the observation of single molecule dynamics.