With plasmonics, light can penetrate solid sheets of metal

Every day, the world finds another way to show us that, once we work on a level that's small enough, nothing makes sense. Things we take for granted no longer happen. For instance, say you're lying in bed in the early morning sunlight - or, no judgment, the late afternoon sunlight. If all that daytime starts bothering your eyes, covering up the window would block the light. Or, if you painted the window green, the room would be suffused with green light.

Once things shrink down far enough, this is no longer the case. If you were in a quantum-scale room and covered the window with a solid sheet of metal, even more light would come streaming in. If you painted the window green, the room would be bathed in red light. Why? Plasmonics.

Plasmons are little electromagnetic waves that move through metals. They allow light to 'fit' in spaces that it would not usually be able to squeeze into. The smallest wavelengths of visible light are around 400 nanometers long. This means that, if a flashlight is turned on a piece of cardboard with a hole less than 400 nanometers wide, no one would be able to see any pinpricks of light shining out the other side. One group of scienctists did an experiment like this, channeling light down an optical fiber that started out with a nice and wide space for light which slimmed down, over the length of the fiber, to 100 nanometers. When the light hit this choke point, it bounced back up the fiber.

That is, it did until scientists brought a gold disk up close to the hole in the fiber. Suddenly, the light shone through. Not only did it leap through a hole too small for it get through, it shone right through the solid gold disk. When the disk was brought close enough to touch the fiber, the light was choked off. When, however, the gold disk was made bigger, even more light came through. Plasmons from the metal managed to yank the light through the too-small opening, and shuttled around the outside of the disk, to the other side, where it continued its journey.

That's not all the weirdness that plasmons have cooked up for us. It's been known that photons can pass through holes in foil much smaller than the light's wavelength, thanks to plasmons. But plasmonics doesn't just depend on size. It depends on color. In one experiment, gold foil with tiny holes only allowed green light to pass through. When the foil was covered with green dye, red light could also pass through the hole. Painting something green turned the light that shone through it red. There's no definitive answer as to why it should be, but since green dye absorbs red light - and every light except green - scientists believe that plasmons work a little like smugglers. The green dye stashes the red light, the plasmons grab it and transport it to the other side of the foil and the dye. There, the light and it goes on its merry way, letting us know that deep down, nothing makes sense.

Via New Scientist and Duke University.