Extraordinary Optical Transmission

Matthew Francis, Ars Technica:

Take a very thin sheet of metal and drill it with tiny holes in a regular rectangular pattern. Ordinarily, if you shine light with wavelength that is larger than the holes, it wouldn’t get through—the metal would be opaque. However, in the case of this particular pattern of holes, a lot of the light gets through the sheet anyway, a phenomenon known as extraordinary optical tranmission (EOT).