Bending Light

[David Morris]

http://rawstory.com/news/afp/A_real_invisibility_cloak_is_in_our_04062007.html

Harry Potter fans take note: scientists have finally come up with a
workable design for an invisibility cloak.

Physicists figured out the complex mathematical equations for making
objects invisible by bending light around them last year.

A group of engineers at Purdue University in Indiana have now used
those calculations to design a relatively simple device that ought to
be able to - one day soon - make objects as big as an airplane simply
disappear.

The design calls for tiny metal needles to be fitted into a
hairbrush-shaped cone at angles and lengths that would force light to
pass around the cloak. This would make everything inside the cone
appear to vanish because the light would no longer reflect off it.

"It looks pretty much like fiction, I do realize, but it's completely
in agreement with the laws of physics," said lead researcher Vladimir
Shalaev, a professor of electrical and computer engineering at Purdue.

"Ideally, if we make it real it would work exactly like Harry Potter's
invisibility cloak," he said. "It's not going to be heavy because
there's going to be very little metal in it."

The still-theoretical design will be published this month in the
journal Nature Photonics.

Shaleav said he needs to secure funding to build the device and
expects it would take two to three years to come up with a working
prototype.

The major limitation is that the current design can only bend the
light of a single wave-length at a time, and does not work with the
entire frequency range of the visible spectrum.

"How to create a design that works for all colors of visible light at
the same time will be a big technical challenge, but we believe it's
possible," Shalaev said. "In principal it's doable."

Even blocking a single frequency can lead to useful applications, Shaleav said.

The cloak could shield soldiers from night-vision goggles which use
only one wavelength of light. It could also be used to hide objects
from "laser designators" used by the military to illuminate a target,
he said.

Other researchers have managed to clock objects from the microwave
range of the spectrum, which are much larger than the wavelengths of
visible light.

This new design is the first for cloaking objects of any size in the
range of light visible to humans.

It works by using tiny needles to alter the "index of refraction"
around the cone.

Every material has its own refractive index which determines how light
bends and slows down as it passes from that material into another.
It's commonly described as the bent-stick-in-water effect, which
occurs when a stick placed in a glass of water looks bent when seen
from outside the glass.

Natural materials typically have a refractive index greater than one.
But the tiny metal needles layered inside the cone work to gradually
alter the index from zero at the inner surface of the cloak, to one at
the outer surface of the cloak. This guides, or bends, light around
the cloaked object.

The technology for making the tiny needles is already used to make
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.

A single nanometer is roughly the size of 20 hydrogen atoms strung together.