Some day we may not need X-rays to see inside people, thanks to a new way to decipher light that passes through opaque surfaces.
Normally visible light becomes too scattered to detect after passing through opaque surfaces. But scientists in France have developed a way to reconstruct images from light passing through such surfaces by deciphering just how the material makes the light scatter.
In the short term the research will help improve the strength of telecommunications signals and fiber optics cables, but years from now the technology could supplement or even replace traditional ultrasounds for baby imaging and X-rays for weapons detection at airports.
"It's like putting a flashlight behind your hand," said Sylvain Gigan, a co-author of the recent Nature Communications and a scientist at the Institut Langevin in Paris. "You cannot see an image, but you can still see a faint glow."
Imagine that there was an image over the top of a flashlight. As the light passes through your hand the image is destroyed; all you see is a faint glow. But using the new method pioneered by the French scientists, they can collect the light and extract an image from it.
Their experiment contained three key pieces of widely available technology: a green laser as the light source, a light modulator (which is often used in projectors), and a charged coupled device, the technology used in many digital cameras.
The laser created the light, which was sent through the modulator, and illuminated the image (in their tests, a rose). The green light bounced off the image and through a glass slide that was painted white, which scatters the light in all kinds of different directions.
Ordinarily that would be the end of it; the image captured by the digital camera would be blurred beyond all recognition. The French scientists got around this limitation by taking picture after picture of the blurred image, and then applying a program that accounts for how the light is scattered by the white glass. That way they could reassemble a grainy image of the flower.
"When light hits a glass of milk, a cloud, or our tissues, some of it is absorbed, but most of it is scattered," said Gigan. "You would think that this light is scattered beyond recovery, but it's not."
It's not imaging as we are used to seeing with X-rays or ultrasounds, said Changhuey Yang, a scientist at Cal Tech familiar with the new research. The image that comes through is grainy and can only work through think opaque surfaces. Nonetheless, Yang said it was "fascinating" that the French scientists could detect an image through a opaque medium.
When doing traditional imaging, like using X-rays to find hidden weapons at airports, "we assume that we know nothing about what is on the other side," said Yang. "In this scenario, this is not the case."
In other words, the French scientists knew what image is supposed to come through. If it were a totally random image coming through the glass it would be much more difficult to detect with their existing technique.
That should be possible one day, said Gigan, but right now its not. When it happens however, the technique could lead to a huge variety of applications.
"What we showed can be adapted to any wavelength," or any kind of wave, said Gigan. At first the technique could help cleanup noise in telecommunciations signals or fiber optic cables. Eventually however, the French scientists hope to adapt their technology to other see-through technologies, such as X-rays or ultrasounds.