Material With Negative Refractive Index Created

holy_calamity writes "The race to build a material with a negative index of refraction for visible light has been won by researchers in Germany. The advance could lead to super-lenses able to see details finer then the wavelength of visible light, or the previously predicted invisibility cloak for visible light." From the article: "[The researcher] determined the refractive index of the material by measuring the 'phase velocity' of light as it passed through. His measurements show the structure has a negative refractive index of -0.6 for light with a wavelength of 780 nm [the far red end of the visible light spectrum]. This value drops to zero at 760 nm and 800 nm, and becomes positive at longer and shorter wavelengths."

Comments

Re:yes, but RTFA, they were not first.

[wolfgang_spangler]

They were first to do this in the 700 nm range but the article state that previously this could only be done in the 1400 nm range. I guess 700 nm is significant because it is the start of the visual spectrum. 700 is red i think. The article agrees with the summary. They were (according to the article) the first to do this for visible light. No claim was made that the German team has created the first ever material with a negative refractive index, just the first material with a negative refractive index for visable light.

Visible spectrum and cones

[benhocking]

Red is ~700 nm and violet is ~400 nm. A typical human can see light from the range of 390-750 nm with the aid of three cones. The three cones are the "red" cone (optimal at 564 nm), the "green" cone (optimal at 534 nm), and the "blue" cone (optimal at 420 nm).

Wikipedia

[benhocking]

Wikipedia does a good job describing refraction and the refractive index. You should try to understand refraction before trying to understand the refractive index.

Group vs. Phase Velocity

[Jazzer_Techie]

When one talks about a wave propagating through a medium, there are two velocities that one usually considers, the group velocity and the phase velocity. The group velocity is the speed at which energy and information are moving. (This isn't always true, but for most materials it is or is a good approximation.) The phase velocity is how fast a "phase" (a feature like a crest) appears to be moving.

A good way to visualize the difference is to think of a ocean waves hitting a wall at an angle. The speed which with the wave itself is moving is the group velocity, but if you look at the wall, you will see the crests moving along at a different speed. (If you have trouble seeing that, make a little sketch.) There is also a nice Java applet (GPLed!) here, which does a good job of illustrating the difference

Re:Can someone explain a refraction index?

[radtea]

Furthermore, it doesn't explain what the basic properties of a positive refraction index are (aside from saying that it's normal), let alone what negative indexes could do.

In ordinary optics, refractive index is the ratio of the velocity of light in vacuum (c) to the velocity in the material (v):

n = c/v

Since v <= c, n >= 1 is always true.

But light, being wavelike, has two velocities associated with it: the phase velocity, which is the velocity of an individual crest in a monochromatic light wave, and the group velocity, which is the velocity of a wave packet consisting of many frequencies. Depending on which velocity you care about, and how you deal with wave packets, it appears that you can extend the definition of refractive index in such a way that negative refractive index is meaningful. The discussions of this that I have seen online are uniformly confusing, so I'm not clear on exactly what is going on, although it is clear that negative extended refractive indices do make sense.

One analogy to think about is the conventional definition of resistance: R = V/I. Clearly by this definition resistance is always positive. But if instead you think of resistance as being the slope of the V/I curve, it is clearly possible for a device whose (conventional) resistance decreases with increasing current it is possible to have a slope that is negative, and this can be treated as "negative resistance". Tunnel diodes exhibit this effect.

If one were to be gloriously pedantic about this, one would only use the terms "negative extended refractive index" and "negative extended resistance", because "negative refractive index" and "negative resistance" are confusing oxymorons to the vast majority of people in the world who are at best familiar with the conventional definitions. And in fact, we usually do make this kind of distinction. We use terms like "electric car" because "car" means "internal combustion engine hydrocarbon-powered road vehicle" to the vast majority of people. Therefore headlines like, "New Car Does Not Need Gasline" would be obviously misleading and confusing if they actually meant "New Electric Car Does Not Need Gasoline."

Re:obligatory

[zero_offset]

It's based upon an episode of The Simpsons.

http://en.wikipedia.org/wiki/Overlord_meme

Original site of the researchers...

[thrill12]

...here, gives (under metamaterials) a good example of what negative refraction is here

Re:Camera lenses

[nokiator]

Technically, this is true, but I am not sure about the reasonable cost part. It is also possible to correct chromatic aberration using diffractive lenses which require much less exotic (at least completely passive) technology. Canon has been able to take the concept of diffractive optics technology to market to manufacture some relatively compact telephoto lenses but even after many years of production, DO lenses are still quite expensive.