Muggles are another step closer to donning a real-life invisibility cloak, as scientists have developed a new technology that can make things invisible under the sun.
Spectral invisibility cloaking renders objects unseen by shifting the frequencies of light that interact with an object.
Scientists have yet to create a full-blown Harry Potter-style invisibility cloak, but the new technology could pave the way for a special device that can make things and people invisible to the naked eye.
How People See Color
The electromagnetic spectrum consists of a vast range of frequencies. These include radiation that cannot be seen with the naked eye, such as X-rays and microwaves.
On one part of the spectrum is a range of frequencies that humans can detect. This is visible light, which itself contains different frequencies that range from red at one end to violet at another.
Some sources of light, such as the sun, have multiple frequencies. These are called broadband sources. When a person sees an object, what he is actually seeing is the interplay between light and the object.
For example, when one sees a red apple, what one is actually seeing is the apple reflecting the red light frequency of the sun. All other colors have passed through, which is why the person cannot see the other colors except for red.
Older Technologies
Researchers at the National Institute of Scientific Research in Montreal, Canada, have developed spectral cloaking, which harnesses the various frequencies of visible light. The new technology was designed to address the limitations set by earlier cloaking techniques.
Older technologies typically involve manipulating the way light interacts with an object by moving the light waves around the object instead of through it.
The different colors of the light would be made to travel around the object in different paths, reaching their destination at different times. The result would be some form of distortion so that the object is not actually fully invisible.
Other technologies do not produce the same distortions, but they are limited to laboratory settings where objects can become visible under only one color of light. Obviously, this would have limited usage in the world illuminated by a broadband light.
Spectral Invisibility Cloaking
In new research published in Optica, the researchers led by telecommunications engineer José Azaña have developed a new device that can make an object invisible by manipulating the frequencies of light as the light wave passes through the object.
The device works by shifting one frequency of light to another as the light passes through the object. Once it has passed, the frequency is put back in its original state. This way, the light passes through the object but does not interact with it at all, making the object invisible to an observer.
For example, if one has a green mango, spectral cloaking would shift the green light frequency to another frequency as light passes through the mango. Once the light has passed, the green light frequency is shifted back in place, rendering the green mango invisible.
The device has two components. Each of these components work by first forcing the light frequencies to move at different speeds and then shifting the specific frequency as the light moves through the object. One of these is placed in front of the object and another is at the back.
The researchers used the device to make an optical filter invisible when illuminated by a beam of laser light. An optical filter reflects certain colors of light while letting other colors pass through. The result was an optical filter that was made invisible under laser light.
"We have made a target object fully invisible to observation under realistic broadband illumination by propagating the illumination wave through the object with no detectable distortion, exactly as if the object and cloak were not present," says Azaña.
Applications For A Spectral Invisibility Cloak
The device is its infancy and has yet to address its own limitations. For now, spectral cloaking only works from one direction. An observer has to be in the path of light so that the object appears invisible to him.
However, the team says it is possible to program the device so that it modifies all frequencies in the entire visible spectrum. This would make an object invisible from every single direction, a goal the researchers hope to accomplish one day.
They are also looking into real-world applications for one-directional invisibility. The researchers say spectral cloaking can be used for security purposes in the military and telecommunications industries.
By using the technology to make fiber optic cables invisible, companies can keep snoops from looking at classified information often delivered as broadband signals through telecommunications lines.
