Magic carpets hide objects in plain sight
THE latest twist on invisibility cloaks won't hide Harry Potter in the middle of a room, but it might just let spies conceal microphones under the rug or the wallpaper.
So called "carpet cloaks" are the first technology to succeed in hiding objects by deflecting light across a range of wavelengths. Two groups described different cloaks last week at the International Quantum Electronics Conference in Baltimore, Maryland.
Invisibility cloaks work by deflecting light waves so the light that reaches the eye shows no trace of the hidden object. Conventional optical materials can't do this, but a dozen years ago John Pendry of Imperial College London showed it was possible to bend light around objects by building materials made of components smaller than the wavelength of the light.
In theory, the principle will work across the electromagnetic spectrum, but early experiments with invisibility cloaks have been done at microwave frequencies, which have wavelengths in the centimetre range, meaning sub-wavelength components are relatively easy to make.
Both new carpet cloaks work in infrared light, which has a wavelength far shorter than microwaves, and provide the first demonstrations of optical cloaking. As they are not limited to a narrow range of wavelengths, in principle the cloaks could hide objects in normal light. Other cloaks, even if scaled down to the optical range, would work only in rooms lit with a single-colour lamp.
The cloaks were made at the University of California, Berkeley, and at Cornell University in Ithaca, New York. Instead of deflecting light waves around an object, both set-ups involve hiding bumps on a thin layer of material. Illuminating the bump from the side would normally cast a dark shadow. But with the cloaks, the light is reflected uniformly so that there is no shadow, and the cloaked surface appears flat (see diagram).
At Berkeley, Jensen Li and colleagues made their invisibility cloak by drilling nanoscale holes into a micrometre-thick layer of silicon. At Cornell, Lucas Gabrielli and colleagues achieved a similar effect by embedding 50-nanometre silicon posts into silicon dioxide.
So far the carpet cloaks only work in two dimensions, but the results are encouraging because the cloaks use only well-known materials and production methods. The demonstrations are "very charming", says Georg von Freymann of the Institute of Nanotechnology at the University of Karlsruhe in Germany. "It looks like real-world applications may come from this."
In the short term, such materials could be used to create new optical devices such as super-lenses for concentrating sunlight. In principle the cloaks might one day hide objects on walls and floors or in satellite images.
So called "carpet cloaks" are the first technology to succeed in hiding objects by deflecting light across a range of wavelengths. Two groups described different cloaks last week at the International Quantum Electronics Conference in Baltimore, Maryland.
Invisibility cloaks work by deflecting light waves so the light that reaches the eye shows no trace of the hidden object. Conventional optical materials can't do this, but a dozen years ago John Pendry of Imperial College London showed it was possible to bend light around objects by building materials made of components smaller than the wavelength of the light.
In theory, the principle will work across the electromagnetic spectrum, but early experiments with invisibility cloaks have been done at microwave frequencies, which have wavelengths in the centimetre range, meaning sub-wavelength components are relatively easy to make.
Both new carpet cloaks work in infrared light, which has a wavelength far shorter than microwaves, and provide the first demonstrations of optical cloaking. As they are not limited to a narrow range of wavelengths, in principle the cloaks could hide objects in normal light. Other cloaks, even if scaled down to the optical range, would work only in rooms lit with a single-colour lamp.
The cloaks were made at the University of California, Berkeley, and at Cornell University in Ithaca, New York. Instead of deflecting light waves around an object, both set-ups involve hiding bumps on a thin layer of material. Illuminating the bump from the side would normally cast a dark shadow. But with the cloaks, the light is reflected uniformly so that there is no shadow, and the cloaked surface appears flat (see diagram).
At Berkeley, Jensen Li and colleagues made their invisibility cloak by drilling nanoscale holes into a micrometre-thick layer of silicon. At Cornell, Lucas Gabrielli and colleagues achieved a similar effect by embedding 50-nanometre silicon posts into silicon dioxide.
So far the carpet cloaks only work in two dimensions, but the results are encouraging because the cloaks use only well-known materials and production methods. The demonstrations are "very charming", says Georg von Freymann of the Institute of Nanotechnology at the University of Karlsruhe in Germany. "It looks like real-world applications may come from this."
In the short term, such materials could be used to create new optical devices such as super-lenses for concentrating sunlight. In principle the cloaks might one day hide objects on walls and floors or in satellite images.
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