National Geographic News
A glass lens and a sugar cube are shown in a picture, each next to a mathematical formula describing how light passes through it.
Decoding the formulas for how specific solids, such as a sugar cube (right), scatter light should allow scientists to see through them as we see through glass (left).

Image courtesy American Physical Society

Charles Choi

for National Geographic News

Published March 10, 2010

Scientists have figured out how to "see" through opaque barriers by unscrambling what little light passes through.

The reason you can't see through thin materials such as dry paint, eggshells, paper, or skin is because any light that manages to pass through them is scattered in complicated and seemingly random ways.

(Related: "See-Through Goldfish Bred; Cuts Out Need for Dissection.")

However, it's actually possible to project light through such opaque materials and reveal objects hidden behind them, according to a new paper by scientists at the City of Paris's Industrial Physics and Chemistry Higher Educational Institution (ESPCI).

The trick is knowing exactly how materials alter light that enters them.

In experiments, the researchers shone a green laser beam at a roughly 80-micrometer-thick layer—that's 80 thousandths of a millimeter—of zinc oxide, a common ingredient in white paints. On the unseen side of the zinc layer were a series of tiny dots.

By analyzing the patterns of light that came through, the physicists generated a complex model called a transmission matrix—essentially a formula decoding the seemingly chaotic way light travels within the opaque material.

By applying the formula, the researchers say, they were able "translate" the green light coming through the zinc oxide, resulting in a digital camera image of dots in shades of green—revealing exactly what was behind the "wall."

(Read about the power of light.)

The team is now attempting to make out far more complex images of familiar objects, though they're awaiting publication before giving specific examples, ESPCI physicist Sylvain Gigan told National Geographic News.

The see-through vision isn't perfect, though, since a lot of light never makes it through to the other side of the opaque material. In more complex, future experiments, this missing "information" might result in grainy images, said Gigan, who co-authored the new study.

(Also see "Two New Cloaking Devices Close In on True Invisibility.")

Sorry, Peeping Toms

The technology will probably never be any good for looking through walls, said physicist Allard Mosk at University of Twente in Amsterdam.

"Looking through a hundred-millimeter [four-inch] wall would be a million times more difficult than looking through a hundred-micrometer layer of paint," said Mosk, who wasn't involved in the new research.

But the method might one day be used to peer into bodies, study co-author Gigan said. The system, though, would need to be thousands of times faster than it is, to compensate for all the scattering generated by the movement of living tissue.

Still, it may become possible to look through several millimeters of skin, the University of Twente's Mosk said. "I think that is still far off but not unrealistic to hope for."

Findings detailed in the March 8 issue of the journal Physical Review Letters.

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