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."

yes, but RTFA, they were not first.

[PrinceAshitaka]

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.

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 [wikipedia.org] and the refractive index [wikipedia.org]. You should try to understand refraction before trying to understand the refractive index.

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

[JesseL]

Slashdot even had a previous article on it (shock!):
http://science.slashdot.org/article.pl?sid=05/04/2 5/1232218 [slashdot.org]

Re:Can someone explain a refraction index?

[Anonymous Coward]

Refractive index is a measure of several things:
(1) Speed of light in a material is (for normal materials where n>1) v = c/n
(2) Measure of how much light bends when it enters said material through something called Snell's law

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 [wikipedia.org] and the phase velocity [wikipedia.org]. 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 [publicliterature.org] (GPLed!) here, which does a good job of illustrating the difference

Re:Can someone explain a refraction index?

[Anonymous Coward]

Short version: light travels at different speeds through different substances. It's faster in air than it is in water or glass. When it strikes a boundary between two substances -- say, air and glass -- at an angle, it will turn slightly, because one edge of the beam hits the new substance sooner than the other, and will slow down (or speed up) sooner.

This is why you sometimes see two of the same fish when you look at the corner of a fish tank. The light gets bent as it travels from water to glass, and again from glass to air, resulting in two paths from the fish to your eye. This is also how lenses work.

So that's refraction. The refractive index is essentially a measurement of how much it bends when pssing into that substance.

(Honestly, I learned about refraction in third or fourth grade. What do they teach in schools these days?)

Re:Can someone explain a refraction index?

[athena_wiles]

Refractive index basically describes how fast light moves through a material. That's the "speed at which they propagate" part of the quote you cited - in materials with a high refractive index, which you might think of more "optically dense" or preventing more barriers to the "movement" of the light, light travels more slowly than it does in materials with lower refractive indices.

When you have two materials with different refractive indices up against each other, light bends by some angle (the angle depends on how close the refractive indices of the two materials are). I'm sure you've seen the effect where you put a straw or a pencil into a partly-full glass of water (if you haven't, go try it) and the straw/pencil appears to be bent - this property of refractive indices is what's causing this phenomenon.

Basically, a negative refractive index changes/reverses the angle at which light bends, which can lead to some pretty funky optical effects. If you go to the wikipedia page on "Metamaterial" there's a diagram indicating this concept.

Does that help? It's not a precise technical definition by any means, but then, I don't think a precise technical definition is what you were asking for, hm? :-)

So the pencil bends the other way now?

[jpellino]

Never mind what this does to the coin-in-the-bowl-of-water trick!

Sheesh.

Re:Can someone explain a refraction index?

[exp(pi*sqrt(163))]

For all I know, it could mean they bend backwards while doing spirals or figure eights.

This is exactly [wikipedia.org] what light does.

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."

Nothing exotic about negative refractive index

[u19925]

There is nothing exotic about negative refractive index. It is trivially achievable in real life experiments, albeit not at optical frequencies. All information about the light falling on any surface can be captured if we can digitize electromagnetic waves at sampling rate which is twice the bandwidth. At optical wavelengths, this would be trillions of samples per second at each sensor and you will need multiple sensors spatially distributed across a surface. At radio frequencies with only a few mega hertz bandwidth, this can be done and is being done routinely (by radio astronomers in VLBI experiments) for almost 30 years. Once you digitize the signal, you can simulate any refractive index as you wish using a computer. Mathematics and computing power are the limit.

Re:obligatory

[Luteus]

http://en.wikipedia.org/wiki/Slashdot#Culture [wikipedia.org]

Re:obligatory

[zero_offset]

It's based upon an episode of The Simpsons.

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

Original site of the researchers...

[thrill12]

...here [uni-karlsruhe.de], gives (under metamaterials) a good example of what negative refraction is here [uni-karlsruhe.de]

Free University

[DerangedAlchemist]

As I understand it, post secondary education has been completely free for the past 200 years.

Re:Is this the actual research paper?

[ultracool]

Papers are typically submitted to arxiv.org at the time of submission to a journal. If accepted, it usually appears in the particular journal several months later. The paper was published in Optics Letters just this week, though it was posted on arxiv.org in August:

http://ol.osa.org/abstract.cfm?id=119886 [osa.org] You have to keep in mind that before Arxiv.org papers (or any other pre-print archives) appear in a journal, you can't guaranteed that they have passed the peer-review process.

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 [canon.com] to market to manufacture some relatively compact telephoto lenses but even after many years of production, DO lenses are still quite expensive [bhphotovideo.com].

Re:Free University

[Anonymous Coward]

Well, this is the last year it'll be free, they will start charging 500 Euro per semester next year. At the same time they are complaining that not enough people are studying... politics in Germany is totally screwed up.

And I'm wondering where the money goes, definitely not to the universities. Some ten universities were selected to become "elite universities". This means that they will see some 10-20 million bucks more per year (in order to compete with Harvard, etc... WTF?). This is a complete joke. They're shooting themselves in the foot.

By the way, this discovery was made at my university, the University of Karlsruhe, and the institute is actually one floor below where I currently am (I'm at the institute for particle physics, working with the CMS detector at CERN).

visual example

[namekuseijin]

In case anyone is wondering what a negative index of refraction would look like, this is a very good start:

http://www.opticsexpress.org/abstract.cfm?id=88325 [opticsexpress.org]

Examples (including avi's) rendered in Povray, the free raytracer. One of the authors is Chris Hormann, one of Povray's main code contributors.

Re:Can someone explain a refraction index?

[Anonymous Coward]

In this, and any case I've heard of, light is not traveling faster than c through a material with a refractive index less than zero. Both the phase velocity and group velocity are less than c. It only means that the group velocity, made of the summation of many monochromatic waves, is in the opposite direction to that of the monochromatic waves themselves.