Light filter lets rays through from only one direction | Science News

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Light filter lets rays through from only one direction

Angle-sensitive device could improve photography and solar energy harvesting

11:07am, March 28, 2014

FILTERED  A device made of glass and tantalum oxide filters light based on its incoming angle. The light ray coming in at 1 o’clock  reflects off the filter. But the other beam streaks right through the device unimpeded.

Like a traffic cop directing cars, a layered stack of transparent materials permits light arriving from only a single direction to pass through. Such angle-sensitive filters could improve cameras and telescopes or allow solar cells to convert sunlight into energy more efficiently.

People have created effective light filters for thousands of years. Stained glass, for instance, filters light by color, allowing only a single shade to shine through while reflecting light at other wavelengths. But scientists have had trouble filtering light based on the angle from which it arrives.

In creating a directional light filter, MIT physicist Yichen Shen and his team knew that for the interface between any pair of materials, light arriving from one specific angle, known as the Brewster angle, can simply pass through unimpeded — it won’t get reflected or bent.

Knowing an interface’s Brewster angle provided a way to allow light from a desired angle to pass

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