Ars Technica: Normally, light does not pass through holes with diameters smaller than the light’s wavelength. However, a specific arrangement of holes in thin metal sheets allows light to pass through the material, in what is known as extraordinary optical tranmission (EOT). Previous experiments have shown that the phenomenon only occurs with metal sheets of a certain thickness and that thinner sheets, counterintuitively, experience less transmission. Two mechanisms are believed to contribute to the effect. Surface plasmon polaritons are the result of the free movement of electrons, on the surface of the metal, that get excited by the light, transmit energy between each other, and emit light on the opposite surface. Quasi-cylindrical waves are the other mechanism; found in electrons, they get excited when struck by light at the holes in the metal. Frerik van Beijnum of Leiden University in the Netherlands and his colleagues experimented with the arrangement of the holes and found that both mechanisms were dependent on the spacing between the holes. Better understanding of EOT will help scientists design more effective optical and biophysical devices that take advantage of the phenomenon.