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Bending light in new ways

Typically, when light moves from one medium to another, say as it travels from air to water, we see it bend from its projected path, a phenomenon known as refraction. Air has an index of refraction of 1, meaning that travels along the same path as it would in a vacuum. But water has a refraction index of 1.33, which means as the light crosses into water it is diverted from its path by a set angle indicated by its index.

Now Princeton University researchers, with the help of National Science Foundation funding, have created a type of material that can bend light in a direction that natural mediums are incapable of doing.

The researchers demonstrated that when a beam of laser light is directed on this material, the light is displaced in an angle such that it can be said to have a negative index of refraction, an angle no natural material could produce.

This material is a type of metamaterial, an emerging class of man-made materials with uniquely engineered properties. According to the Princeton press release, previous metamaterials "were two-dimensional arrangements of metals, which limited their usefulness. The Princeton invention is the first three-dimensional metamaterial constructed entirely from semiconductors."

The work may pave the way for improved glasses and other optical focusing instruments.

With metamaterial-based lenses, microscopes will be able to view objects as small as a string of DNA. It is the curve in a lens of today's microscopes that limits resolution at very fine levels. The curve compensates for positive refraction, but limits resolution. With this material producing, in effect, negative refraction, it doesn't need to be curved.

Also, this work could bring about more finely-tuned environmental hazard sensors. Other researchers are looking to build tiny sensors that can monitor for trace amounts of gases. The wavelength of the light beam (infrared) this material refracts is about the same width as that of the gas molecule, so detection of very small trace elements of some deadly gas can be done at low cost, by simply checking for disruptions of the wavelength.

As EE Times noted, the material could be used in optical communications as well. We could fit more telephone calls and Internet traffic on a single fiber optic line, as the material could more precisely control the infrared wavelengths these signals are encoded in. This is not such a big need as we don't fill up our current fiber optic lines even today. But in 10 to 15 years, when this material should become production ready, it may be a concern.

And while most of the news coverage didn't mention this as a possibility, we also imagine these metamaterials could also be used to produce improved lens for astronomy, as that field has always been hampered by distortion issues.

Wired News speculated that a cloaking device could be built from this material, but admitted such a device would be generations away.

Posted by Joab Jackson on Oct 18, 2007 at 9:39 AM


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