How to trap a rainbow

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London, November 27 (ANI): In a new research, scientists have used a convex lens to trap a rainbow for the first time.

In 2007, Ortwin Hess of the University of Surrey in Guildford, UK, and colleagues proposed a technique to trap light inside a tapering waveguide, which is a structure that guides light waves down its length.

The waveguide in question would use metamaterials - exotic materials that can bend light sharply.

The idea is that as the waveguide tapers, the components of the light are made to stop in turn at ever narrower points.

That's because any given component of the light cannot pass through an opening that's smaller than its wavelength.

This leads to a "trapped rainbow".

While numerical models showed that such waveguides would work in theory, making them out of metamaterials remained a distant dream.

Now, according to a report in New Scientist, Vera Smolyaninova of Towson University in Baltimore, Maryland, and colleagues have used a convex lens to create the tapered waveguide and trap a rainbow of light.

They coated one side of a 4.5-millimetre-diameter lens with a gold film 30 nanometre thick, and laid the lens - gold-side down - on a flat glass slide which was also coated with film of gold.

Viewed side-on, the space between the curved lens and the flat slide was a layer of air that narrowed to zero thickness where the lens touched the slide - essentially a tapered waveguide.

When they shone a multi-wavelength laser beam at the open end of the gilded waveguide, a trapped rainbow formed inside.

This could be seen as a series of coloured rings when the lens was viewed from above with a microscope: the visible light leaked through the thin gold film.

Shorter-wavelength green light was trapped at a point where the taper became too thin for it to penetrate the waveguide.

Longer-wavelength red light was trapped further out, where the taper was thicker, with intermediate wavelengths in between

"I think it's beautiful that we can create such complex phenomena using a very, very simple configuration. It's amazing," said Smolyaninova. (ANI)

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