Researchers build optical invisibility cloak for a diffusive medium: ...The tank was filled with a white, turbid liquid. Objects inside cast a visible shadow onto the tank wall. Simple metal cylinders or spheres of a few centimeters in diameter were used as test objects... To pass the light around the object, the researchers applied a thin shell made of the transparent silicon material PDMS, to which a certain concentration of light-scattering melamine microparticles was added. The silicon/melamine shell caused a quicker diffusion than in the environment and, thus, passed the light around the objects...
"Ideal optical invisibility cloaks in air have a drawback... They violate Albert Einstein's theory of relativity that prescribes an upper limit for the speed of light. In diffuse media, in which light is scattered several times, however, the effective speed of light is reduced. Here, ideal invisibility cloaks can be realized."
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