Ability to transfer images through opaque material
Physicists from France have succeeded in reconstructing a primitive image projected with a laser onto a painted plate by placing a CCD camera on the other side of the obstacle.
Some objects that seem opaque to us actually transmit light, but the scattering of radiation does not allow us to understand what is behind such objects. In 2007, scientists from the Netherlands, however, managed to focus the radiation passing through the eggshell and the human tooth.
The authors tried to develop the idea of these experiments and used a glass plate coated with a layer of paint 80 ± 25 μm thick as an opaque material. In order to reconstruct the projected image, it is necessary to know exactly how the radiation is scattered (to define the so-called transmission matrix). “If [слой краски] imagine in the form of a labyrinth, which must overcome the light, then the transmission matrix will turn out to be a map of this labyrinth, ”explains research participant Sylvain Gigan.
In the process of drawing up the matrix, scientists had to direct the laser radiation at a wavelength of 532 nm to the plate more than a thousand times, each time slightly changing the beam parameters using a spatial light modulator. The camera on the opposite side recorded the scatter diagrams, and the experimenters compared the results with the effect on the radiation that was specified, and calculated the parameters of the matrix.
Experiment scheme. SLM – spatial light modulator, L – lens, P – polarizer, D – diaphragm. (Illustration by the authors of the work.)
After that, the simplest image, consisting of only 256 pixels, was projected onto the opaque sample; a person looking at the plate will see only an even glow, but the authors, knowing the parameters of the transmission matrix, successfully reconstructed the image details. “The renovation process is going very quickly,” says Mr. Gigan. “Almost as fast as video frames.” So far, however, this technology is extremely far from practical use: the transmitted 256-pixel images are just a background against which several pixels of increased brightness stand out.
Reconstruction of images with one and two highlighted points (illustration by the authors of the work).