Invisibility devices have captured the human imagination for many years. Recent theories have proposed schemes for cloaking devices using transformation optics and conformal mapping. Metamaterials with spatially tailored properties have provided the necessary medium by enabling precise control over the flow of electromagnetic waves. Using metamaterials, the first microwave cloaking has been achieved but the realisation of cloaking at optical frequencies, a key step towards achieving actual invisibility, has remained elusive. Now a team led by Xiang Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center, USA, has created a “carpet cloak” from nanostructured silicon that conceals the presence of objects placed under it from optical detection. While the carpet itself can still be seen, the bulge of the object underneath it disappears from view. Shining a beam of light on the bulge shows a reflection identical to that of a beam reflected from a flat surface, meaning the object itself has essentially been rendered invisible. The carpet cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. The cloak consists only of isotropic dielectric materials, which enables broadband and low-loss invisibility at a wavelength range of 1400 –1800 nm.

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