Invisibility extends out of its shell

[n2doc]

Step inside and, at least at a certain wavelength, light would flow smoothly around you as though you were hardly there — that was thinking behind the world’s first “invisibility cloak” which was unveiled a couple of years ago. The catch was that, with no light entering the cloak, the inability of people to see you on the inside would be matched by your inability to see them on the outside.

Now, a team led by Che Ting Chan at the Hong Kong University of Science and Technology claims to have solved this problem with a theoretical device that can cloak an object from a distance. The idea is that the cloak uses an in-built copy of the object to control how the cloak cancels the external scattering of electromagnetic waves. When light shines on the cloak and the remote object, both of them are invisible.

Light geometry

The invisibility cloaks built since 2006 have been based on a shell of material with a non-uniform, negative refractive index to guide light in curved lines. But it is not easy to figure out how to design the shell’s refractive-index profile so that the light can propagate neatly around a finite volume. The trick is to see the material as something that can perform a transform from cartesian co-ordinates, in which light travels in straight lines, to curved co-ordinates. Coupled with James Clerk Maxwell’s theory of electromagnetism, such transforms can provide a blueprint for a device that leaves a “hole” in space.

more:

http://physicsworld.com/cws/article/news/36633;jsessionid=6126CBB2C9E5462D037FE0F91EAD0480

[Xipe Totec]

1. negative refractive index means that light is actually traveling faster than light

it's going around the object in the same time it would have taken to travel through it.

Ponder that, and let it sink in...

:wow:

[Arctic Dave]

3. Hmmmm. Time travel. Nice pick up.

[caraher]

4. No it doesn't

The negative index means that the light refracts in the opposite direction from its behavior in a material with a positive index, per Snell's Law (n1 sin theta_1 = n2 sin theta_2).

The negative sign does indicated a wave whose phase velocity is opposite the direction of propagation of energy, which is pretty mind boggling.

What you say would be true not of a negative index material, but a material whose index was less than 1. (Or maybe I should say whose absolute value is less than 1!) In a medium light propagates with a speed of v=c/n; for |v|>c you need |n|<1, not n<0.

[Xipe Totec]

6. Party pooper

I bet you oppose the repeal of the 3rd law of thermodynamics too!

[Arctic Dave]

2. Why not just ask the Klingons how they do it. :)

[caraher]

5. more basic info on negative index materials

A Duke researcher's primer on the topic