‘X-ray specs’ for visible light

Researchers from the Netherlands and Italy have succeeded in making sharp pictures of objects hidden behind an opaque screen.

The reason, of course, that materials such as paper appear opaque is because they scatter light, rather than allowing it to move in a straight line.

In the past, methods have been developed to retrieve images through materials in which a small fraction of the light follows a straight path – but it’s never before been possible to resolve an image from light that has been completely scattered.

Now, though a team from the University of Twente in the Netherlands has succeeded in doing just this.

The researchers scanned the angle of a laser beam that illuminated an opaque diffuser. At the same time, a computer recorded the amount of fluorescent light that was returned by a tiny object hidden behind the diffuser.

“While the measured intensity of the light cannot be used to form an image of the object directly, the information needed to do so is in there, but in a scrambled form,” explains Dr Allard Mosk.

“The two young scientists who are the first authors of this paper had the brilliant idea to find out whether that scrambled information is sufficient to reconstruct the image – and they found a way to do so.”

The method involves using a computer program that initially guesses the missing information, and then tests and refines the guess. And, in this way, the team succeeded in making an image of a hidden fluorescent object just 50 micrometers across.

The researchers expect their work to lead to new microscopy methods capable of forming razor-sharp images in a strongly scattering environment.

“This will be very useful in nanotechnology,” says Mosk. “We would like to bring structures to light that are hidden inside a complex environments like computer chips.”

They’d also like to extend their method to examine objects under the human skin. “But for the moment,” says Mosk, “our method is too slow for that.”