Forget about fancy metamaterials that can make microscopic objects invisible–researchers at two different universities have independently shown that larger objects can be rendered invisible using a mineral that’s both naturally occurring and common: calcite.
This latest step in physicists’ ongoing quest to create an invisibility cloak come from an MIT lab, with a paper published in Physical Review Letters, and a University of Birmingham lab, whose paper just came out in Nature Communications. Both teams explained that they used calcite to make objects that are large enough to be seen with the naked eye invisible.
“By using natural crystals for the first time, rather than artificial metamaterials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light,” said Shuang Zhang, the University of Birmingham physicist who led the research…. “This is a huge step forward as, for the first time, the cloaking area is rendered at a size that is big enough for the observer to ‘see’ the invisible object with the naked eye.” [BBC]
The researchers constructed their cloaks from two glued-together calcite crystals, which have a convenient optical property called birefringence–that means they can bend a ray of light in two different directions. Then they placed the objects to be concealed in a notch beneath the crystals.