Photonics - More than transparent

The usual experience is that hardly any radiation will penetrate a metal plate with holes in it that are smaller in diameter than the radiation's wavelength. It comes a surprise then that thin, perforated silver films deposited on quartz are remarkably transparent to radiation at certain wavelengths, selectively and strongly retransmitting it at wavelengths greater than the hole diameter. The explanation for this extraordinary behaviour seems to rest with the excitation of surface modes called surface plasmons, which are oscillating electromagnetic fields localized at the metal surface. The practical use of the phenomenon could be in radiation-filtering devices.