Why light passes through tiny holes

17 Jun 2002

Plasmons play key part in new theories for light transmission through an array of holes

Two separate research groups have offered explanations for a baffling experiment that was published three years ago, in which much larger amounts of light than expected were seen to pass through a silver-coated quartz barrier that contained a periodic array of 150 nm-diameter holes.

At the time, researchers correctly guessed that the light was able to pass through the owing to surface plasmons - non-radiating electromagnetic disturbances arising from the collectivemovements of electrons at conductor-insulator interfaces.

New research from an international group based at the Queen's University of Belfast , UK, and led by Salomon suggests that the light is transmitted through these subwavelength holes as a result of the plasmons and the light photons forming a composite object known as a surface plasmon polariton. The combination of the plasmon polaritons with the regular arrangement of holes results in a crystal-type arrangement, which the group calls a "polaritonic crystal" - with an electromagnetic field that is at its most intense close to (or at) the location of the holes. According to one of the researchers, Anatoly Zayats, the polaritonic crystal is highly analogous to photonic crystals and could have a similar host of applications.

Another group, based at the University of Zaragoza in Spain, has shown that the transmission is made possible by a pairing of surface plasmons that leads to a molecule picture of the process as opposed to a crystal picture. Both discoveries are to be revealed in a forthcoming issue of the journal Physical Review Letters.