Optical cloaks hide objects in broad daylight: Now two different cloak designs have managed to conceal bumps over the full visible spectrum. Chris Gladden and Majid Gharghi of the University of California, Berkeley, etched holes into a thin layer of silicon nitride deposited on porous glass. Varying the diameter of the holes between 20 and 65 nanometres – smaller than the wavelengths of visible light – changed the way the layer refracted light, allowing its interaction with the porous glass substrate to cloak a small bump...
Earlier this year, Baile Zhang and colleagues at the Singapore-MIT Alliance for Research and Technology achieved a similar effect with polarised light, whose electric field is lined up in one direction. The team aligned calcite crystals, which have refractive properties that depend on the electric field's direction, to hide a 2-millimetre-high bump
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