Scientists use natural light to see around corners

Weizmann researchers develop a unique imaging technique to “turn walls into mirrors” using natural light instead of lasers.

July 18, 2012 04:50
2 minute read.
ORI KATZ, Eran Small, Prof. Yaron Silberberg

ORI KATZ, Eran Small, Prof. Yaron Silberberg. (photo credit: Courtesy Prof. Yaron Silberberg)

Scientists at the Weizmann Institute of Science have developed a unique imaging technique to “turn walls into mirrors” using natural light instead of lasers and to “see around corners.”

The work, performed by Prof. Yaron Silberberg and colleagues at the Rehovot institute, was published on Monday night in the prestigious journal Nature Photonics.

Photonics researchers in recent years have tried to correct the “scattering” of light that causes objects to be opaque or non-reflecting. But the Weizmann scientists – members of the institute’s Ulra Fast Optics Group – have used a “spatial light modulator” (SLM) to eliminate the scattering.

“If you want to look to see an embryo developing inside an egg but the eggshell scatters everything, or you want to look through the skin, scattering is the main enemy there,” Silberberg said. He and students Ori Katz and Eran Small used a technique called wavefront shaping to use SLMs to make scattered light refocus at a different location.

SLMs are made up of pixels that can correct for this by using an electric field, slowing down some sections of the beam and allowing others to go through unchanged. The researchers went on to bounce light off an object as in reflection instead of it passing through a scattering material.

But the team then realized that the same approach can work in reflection – that is, not passing through a scattering material but bouncing off of it, such as the case of light bouncing off a wall at a corner. This in effect turns an opaque object into a reflective mirror. The development can be used for a variety of applications, including new medical lasers, optical microscopes and astronomy work conducted from earth.

Ultra-focused lasers have been used for decades to cut metal cleanly and precisely.

These “laser knives” can replace metal scalpels. They are also used in some kinds of medical imaging and are part of advanced optical microscopes.

Many of these uses require the light to be focused tightly to a very narrow, highly intense point. This is one way of cutting cleanly without causing harm to the surrounding area.

This is fine when the target point is on an exposed surface.

But scientists and surgeons prefer to aim lasers under the skin as well, such as targeting tumors in the body. Yet a standard laser can’t focus even a millimeter under the skin, because biological tissue is opaque rather than transparent, causing the light entering it to scatter in all directions.

This weakens its intensity, and the laser is no longer able to slice cleanly through living tissue.

Silberberg’s team thus looked for a way to focus rapid flashes of laser light as they pass through a scattering layer. They created a system that can assess, in real time and using feedback, how the light scatters.

Using algorithms they developed, they created a beam that can “anticipate” the dispersal of its light and make the necessary corrections.

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