These electron microscope images show an experiment in which Princeton Professor of Engineering Stephen Chou showed that blocking a hole in a thin metal film could cause more light to pass through the hole than leaving the hole unblocked. The top image shows an array of 60nm holes spaced 200nm apart with gold caps, each of which is 40 percent bigger than the hole on which it sits. The bottom image shows a cross-section view of one hole with the cap sitting on top of SiO2 pillar. The gold film in the experiment was 40nm thick. The hole covered with the cap surprisingly allows 70% more light to be transmitted through the film than a hole without the cap, Chou's research team found.
"We did not expect more light to get through," Chou said. "We expected the metal to block the light completely."
Chou said the metal disk acts as a sort of "antenna" that picks up and radiates electromagnetic waves. In this case, the metal disks pick up light from one side of the hole and radiate it to the opposite side. The waves travel along the surface of the metal and leap from the hole to the cap, or vice versa depending on which way the light is traveling. Chou's research group is continuing to investigate the effect and how it could be applied to enhance the performance of ultrasensitive detectors.
Thanks to JM for sending me the link!