Someday You'll Keep A Rainbow In A Cage

Scientists have been able to use metal to do tricks with light. Now they can differentiate that light into a spectrum, and store each colour in separate little grooves on the metal. With the power of plasmonics, you may one day have a rainbow on your keychain.

Image via Ortwin Hess

Plasmonics is a branch of physics that, with the push towards quantum and optical computing, is gaining more and more interest. Practically speaking, plasmonics is another example of how things behave very, very strangely at small scales. For instance, if a hole too small for visible light to get through is blocked by a piece of gold foil, suddenly light shines out the far end of the gold foil. The larger the foil is, the more light shines through. Plasmonics have also been used to create the world's tiniest laser.

Plasmonics help shrink down the already-tiny world of light. Plasmons, little ripples of energy in the surface of a metal, interact electromagnetic waves and keep, or move them through, a hollow space otherwise too small for them to fit into. Researchers used this property of plasmonics to temporarily trap a rainbow. They etched grooves into a tiny piece of silver, each groove slightly deeper than the last. They then shone light over the surface, letting some of it interact with the plasmons on the silver. They found that the grooves trapped different wavelengths of light from 500-700 nanometers. About 400-700 nanometers is the visible light spectrum, so this rainbow was missing out on deep purples and blues, but they did manage to get consecutive wells of coloured light. Sadly, the process caused a loss of metal at the surface of the silver, so for now, light is only slowed, not trapped forever. Once someone manages to compensate for the loss of metal, people could buy themselves a pocketful of rainbows.

Read the full scientific paper Proceedings of the National Academy of Sciences.