Invisibility Undone: Chinese Scientists Demonstrate How To Uncloak An Invisible Object

By | December 1, 2008

Harry Potter beware! A team of Chinese scientists has developed a way to unmask your invisibility cloak. According to new research, certain materials underneath an invisibility cloak would allow invisible objects be seen again. … Invisibility as it has been achieved so far in the laboratory is very limited. It works, but only for a narrow band of light wavelengths. Nobody has found a way yet to make an object invisible to the broad range of wavelengths our eyes are attuned to seeing, says Chen, and doing so would be a challenge.

An even greater problem for anyone who has aspirations to be concealed in public one day is that invisibility achieved through transformation media is a two-way street. With no light penetrating a perfect invisibility cloak, there would be no way for an invisible person to see outside. In other words, invisible people would also be blind—not exactly what Harry Potter had in mind.

But now, Chen and his colleagues have developed way to partially cancel the invisibility cloak’s cloaking effect. Their “anti-cloak” would be a material with optical properties perfectly matched to those of an invisibility cloak. (In technical jargon, an anti-cloak would be anisotropic negative refractive index material that is impedance matched to the positive refractive index of the invisibility cloak).

While an invisibility cloak would bend light around an object, any region that came into contact with the anti-cloak would guide some light back so that it became visible. This would allow an invisible observer to see the outside by pressing a layer of anti-cloak material in contact with an invisibility cloak.

“With the anti-cloak, Potter can see outside if he wants to,” says Chen, who conducted the research together with his colleagues at Shanghai Jiao Tong University and The Hong Kong University of Science and Technology. … – sd

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