Washington, Apr 3 (ANI): Researchers are using nanotechnology to create a Harry Potter type optical cloaking device that can render objects invisible by guiding light around anything placed inside the cloak.

Purdue University engineers, following mathematical guidelines devised in 2006 by physicists in the UK, have created a theoretical design that uses an array of tiny needles radiating outward from a central spoke.

The design, which resembles a round hairbrush, would bend light around the object being cloaked.

Background objects would be visible but not the object surrounded by the cylindrical array of nano-needles, said Vladimir Shalaev, Purdue's Robert and Anne Burnett Professor of Electrical and Computer Engineering.

The design does, however, have a major limitation: It works only for any single wavelength, and not for the entire frequency range of the visible spectrum, Prof. Shalaev said.

But this is a first design step toward creating an optical cloaking device that might work for all wavelengths of visible light, he said.

According to Prof. Shalaev, calculations have also indicated that the device would make an object invisible in a wavelength of 632.8 nanometres, which corresponds to the colour red.

The same design could also be used to create a cloak for any other single wavelength in the visible spectrum, he said.

How to create a design that works for all colours of visible light at the same time will be a big technical challenge, but we believe it's possible. It is clearly doable. In principle, this cloak could be arbitrarily large, as large as a person or an aircraft, Prof. Shalaev added.

What we propose is the cloaking of objects of any shape and size. Two requirements are needed to render an object invisible: Light must not reflect off of the object, and the light must bend around the object so that people would see only the background and not the cloaked object itself.

If you satisfied only the first requirement of preventing light from reflecting off of the object, you would still see the dark shadowlike shape of the object, so you would know something was there. The most difficult requirement is to bend light around the cloaked object so that the background is visible but not the object being cloaked. The viewer would, in effect, be seeing around, or through, the object, he said.

Prof. Shalaev said the device would be made of so-called non-magnetic metamaterials.

Meta in Greek means beyond, so the term metamaterial means to create something that doesn't exist in nature. Unlike designs for invisibility in the microwave range, the new design has no magnetic properties. Having no magnetic properties makes it much easier to cloak objects in the visible range but also causes a small amount of light to reflect off of the cloaked object, he said.

But this could, in principle, be offset by other means, for example, with antireflective coatings. The big challenge is how to make rays bend around the object, which we have described how to do in this paper.

A key factor in the design is the ability to reduce the index of refraction to less than one. Refraction occurs as electromagnetic waves, including light, bend when passing from one material into another. Natural materials typically have refractive indices greater than one. The new design reduces a refractive index to values gradually varying from zero at the inner surface of the cloak, to 1 at the outer surface of the cloak, which is required to guide light around the cloaked object.

Creating the tiny needles would require the same sort of equipment already used to fabricate nanotech devices. The needles in the theoretical design are about as wide as 10 nanometers, or billionths of a meter, and as long as hundreds of nanometers. They would be arranged in layers emanating from a central spoke in a cylindrical shape. A single nanometer is roughly the size of 20 hydrogen atoms strung together, Prof. Shalaev said.

Prof. Shalaev further said though the design would work only for one frequency, it still might have applications, such as producing a cloaking system to make soldiers invisible to night-vision goggles.

Since night-imaging systems detect only a specific wavelength, you could, in theory, design something that cloaks in that narrow band of light, Prof. Shalaev said.

The research is based at the Birck Nanotechnology Center at Purdue's Discovery Park, and the findings are detailed in a paper appearing this month in the journal Nature Photonics. (ANI)