Physicists scale up invisibility cloaks using natural crystals

Physicists from the University of Birmingham, with colleagues at Imperial College, London, and Technical University of Denmark, have demonstrated an 'invisibility cloak' that can hide a three-dimensional object, centimetres in dimension, large enough for the cloaking area to be visible to the human eye, according to research published today (1 February 2010) Communications. The scientists have shown that they are able to hide an object that is much bigger than those cloaked by other research groups. Previous studies have demonstrated cloaking by using a metamaterial - a fabricated composite with optical properties not found in nature - which limits the size of the cloaking region, while the team from UK and Denmark have used a natural crystal called calcite, which has enabled them to hide a larger object. Calcite is a transparent mineral with birefringent or double-refraction properties, which means that light enters the calcite and splits into two rays of different polarizations travelling at different speeds and in different directions. The team has been able to cloak larger objects because it has employed a cloaking design that did not require inhomogeneous material properties, as all the previous works did. This demonstration was performed, both in the air and in a container of liquid, by using two triangular pieces of calcite glued together, placed on a mirror. The size of the cloaking area is not limited by the technology available, only by the size of the calcite crystal.