Opaque materials are used for a wide variety of applications, ranging from creating doors that are neither see-through, nor completely closed off, paints, fabric, paper, biological tissue and so on. While in some instances it is useful to have an opaque material, in other cases scientists are struggling hard to surpass this limitation. The reason why light does not pass through these materials is the fact that they tend to scatter incoming photons, to the point where the information they encode – the image that is behind the material – is lost. Now, experts devise a new means of exceeding this limitation.
“"It is possible to see the light, but not the information. We wanted to create a way to see the information through opaque media,” told
PhysOrg in an interview Sylvian Gigan, who is a research scientist at the City of Paris Industrial Physics and Chemistry Higher Educational Institute (ESPCI). Together with a number of colleagues, the expert set out to demonstrate through an experiment that a transmission “matrix” capable of seeing through opaque materials can indeed be built. “When people try to look into an opaque medium, especially biological material, they use the ballistic light, the light that has not been mixed up by the medium due to scattering. But as you go into the medium, the ballistic light becomes less intense, limited by the scattering process,” he explains.
Details of the research appear in a paper entitled “Measuring the Transmission Matrix in Optics: An Approach to the Study and Control of Light Propagation in Disordered Media,” which was published in the latest issue of the respected scientific journal Physical Review letters. What the team basically did in the new study was find a way to use scattering to their benefit, rather than working to defeat its effects. The researchers shone light on zinc oxide, which is a very common chemical found in paint. They then analyzed the scattering patterns, and developed an accurate mathematical model to describe the way photons move. Gigan says that, once the transmission matrix is obtained, then analysis of whatever information passes through the opaque material becomes possible.
The group reveals that the method is also reversible, which means that a beam of light could be made to pass through an opaque material, and then focused once on the other side. This could be of tremendous help to biologists, who are desperately trying to exceed this limitation in order to image biological systems. “This provides a way to transmit information or focus light in a medium that wouldn’t by any classical means allow that,” the team leader says.
But the new observations method does have its limitations, the group admits. “This should not be construed to mean that we can see through walls with this technique. Some degree of light has to be able to pass through, and a wall stops light from coming out the other side. You could use white fabric, paint, or paper, though. Even biological tissue, like a chicken breast, could work,” Gigan concludes.
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