Tuesday, November 22, 2011

Why invisibility cloaks may be in our future

At one point, even just the idea of having the ability of invisibility was a fictional concept. But what if you really could? Would you use the ability for good or evil? This is something Cian, one of my characters, has to deal with. After an experiment goes wrong and he finds himself invisible to the world, at first, he finds it fun...until time passes and loneliness kicks in.

But what if you didn't have to be 'changed' to be invisible? What if you just had to put on a cloak to be hidden from the world? If you've watched Harry Potter, Harry receives one as a gift that he uses to sneak around Hogwarts.

While the first invisibility cloaks worked at microwave frequencies, physicists have found a way to create a cloak that works by hiding events in time. It's made possible because of a duality between space and time in electromagnetic theory (or rather-- the diffraction of a beam of light in space in mathematically equivalent to the temporal propagation of light through a dispersive medium). Like a lens focusing light in space using diffraction, it's also possible to use dispersion to make a lens that focuses in time.

Such a time-lens can be made using an electro-optic modulator, for example, and has a variety of familiar properties. "This time-lens can, for example, magnify or compress in time," say Fridman and co.

The trick, the physicists realized to creating a temporal cloak, was to place two time-lenses in series and then send a beam of light through them, compressing the light in time while the second decompresses it again. For a short period of time, they found that there's a hole in time where to the observer, because of the light coming out of the second time-lens, it appears undistorted as if nothing occurred. However, this method has some limitations, such as lasting only for 110 nanoseconds.

A second method was found more recently in which, researchers From the University of Texas created a cloak, using the technique of a mirage effect to hide objects from view, even creating an on and off switch to make it work.

A mirage effect is naturally occurring in which light rays are bent to produce a displaced image of distant objects. It can happen, for instance, when there's a big change in temperature over a small distance, bending the rays so that they are sent toward the eye rather than bouncing off the surface.

So if you see a pool of blue water in the middle of the desert it’s just the blue sky being redirected from the warm ground and sent directly into your eye. Your brain swaps this mad image out for something more sensible: a pool of water.

The scientists decided to find a material that would have an ability to conduct heat and quickly transfer it to surrounding areas to mimic the light-distorting temperature gradients of the desert. What they found was that sheets of carbon nanotubes that are one molecule thick, wrapped into cylindrical tubes, have a density of air but the strength of steel. Because they are also excellent conductors, the scientists believed that they would make the ideal material to create this mirage effect. Through electrical stimulation, the transparent sheet of nanotubes were quickly heated to high temperatures, transferring the heat to its surrounding areas. This caused the light rays to bend away from the object that was concealed behind the device, making it appear invisible.

"We really can hide objects. ... We can switch for a short moment and make it disappear," said Ali Aliev, a physicist at UTD.

While the technology is limited to the lab at the moment, researchers hope that in time the material could be used to hide large objects, such as military tanks. This still doesn't mean, however, that a human could wear such a device. At this time. But if something was created for a human to actually wear, what would you do with it?

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