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A rough road to lensless imaging.

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Unlike a mirror, a rough surface reflects light in random directions. But that scattered light can still carry information. Researchers have now discovered that they can retrieve an image from the light scattered by a rough surface, without using a lens or a curved mirror to focus the light.

To demonstrate the effect, Paul Rochon and Daniel Bissonnette of the Royal Military College in Kingston, Ontario, shine light on a slide (see diagram). Light emerging from the slide's transparent areas diverges and passes through a beam splitter, which allows about half the light to reach a screen with a rough surface. The beam splitter intercepts light scattered back toward the slide and redirects it to a detector, where the researchers find a reasonably faithful image of the object originally depicted on the slide. This image appears as a bright, somewhat fuzzy region superimposed on a dimmer, relatively uniform back round of scattered light.

"We found we could do it quite easily," Rochon says. "We started with a point source reflected off a white piece of paper. We could actually see the image."With a detector known as a charge-coupled device, they picked up images of more complicated objects, such as letters of the alphabet. Rochon and Bissonnette describe their findings in the Dec. 20,1990 NATURE.

The researchers are now investigating what factors influence image resolution. They have already experimented with a variety of light sources, including lasers and tungsten lamps, and with different rough reflectors, such as diluted latex paint and microscopic polystyrene spheres suspended in water. Rochon and Bissonnette are also looking into the possibility of detecting an analogous effect when a rough surface scatters sound waves.

(Figure Omitted)
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Publication:Science News
Date:Jan 19, 1991
Words:282
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