Holey metal, Batman! Extraordinary optics make it appear transparent

Warner Bros. / Aurich Lawson

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). Since the discovery of EOT, the effect has been harnessed in a number of optical and biophysical devices. A full theoretical understanding of the phenomenon proved elusive, however, which could hamper further device development.

A systematic exploration of hole spacing may help elucidate the mechanism behind EOT. Frerik van Beijnum and colleagues demonstrated that electrons on the metal's surface have two properties that contribute to EOT, with different strengths depending on the hole density and configuration. These results enabled the researchers to determine the physical parameters that dictate EOT, potentially leading to new device designs.

Ordinarily, light can pass through an opaque barrier only if the barrier is pierced with openings larger than the light's wavelength. (This also applies to all manner of waves, including sound and water waves.) That's why EOT is fascinating: the holes are smaller than the wavelength, yet a substantial amount of light still gets through something that would ordinarily be opaque. Oddly, making the material thinner—and therefore more transparent—decreases the EOT effect.