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 than 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.

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.

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.

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

I actually achieved this a couple of years ago. But the phone rang and I set it down somewhere, and now I can't find it.

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

You can't find the phone? It's probably under your invisibility cloak. Try the pager from the base.

Visible spectrum and cones

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).

Re:Visible spectrum and cones

Yes, the "far red end". Finally, I shall have my revenge. There shall be no more red. My fellow color-blind brethren rejoice. No longer will they laugh and point at us. That's not green! You idiot! Idiot? I think not. Our time is now.

This will revolutionize...

small penis jokes at physics conventions.

All right!

Nothing to see here. Move along.

Finally...

An invisibility cloak..

For the first time, I may have a real shot at seeing real life naked boobies

This should come in handy...

!!!tsoP tsriF

Invisibility cloak?

I can understand how this material can make an item stealthy from radars and all. This material can be used to bend / deflect the rays so that they never return to the radar. But the same concept does not an invisibility cloak make. If a cloak deflects light, then the human eye will see a missing spot (Because, unlike the radar, an eye would see everything else around the cloak).

So, for a cloak to be invisible, we need it to pass light from the other end of the cloak. For this, the cloak would need to know the geometrical shape that it has currently, absorb light coming from one end, and forward it to a light emitting object on the other end of the cloak. The problem then will be that the cloak would need to know where the "eye" is to be able to map back and front ends correctly.

Am I talking non-sense here?

Re:Invisibility cloak?

What left-handed materials do is that it bends light in the opposite sense that we are accustomed. For example, if you place a pencil in a glass of water, the refraction of light will make the pencil appear shallower than its true position. If the pencil is placed in a left-handed medium, then the pencil will appear deeper than it actually is.

What happens is that left-handed (aka negative refractive index) materials will bend light away from the surface of the material instead of towards it. So making an "invisibility cloak" is not that hard. First off, to solve the problem of knowing where the eye is, you simply make the surface of the material symmetric. So for a three-dimensional object, the left-handed material needs to be spherically symmetric. They have produced an example in the microwave region for a cylindrically symmetric configuration. But the cylindrical symmetry means that the shroud will only work for certain polarizations of light.

So what happens is that when light hits the curved surface, instead of being bent in towards the center, it is bent outwards. If the refractive properties of the medium are properly tuned, what you end up doing is bending the light around the obstacle such that it leaves the medium in the same path that it would have without the obstacle. So the "invisibility cloak" works by bending light around and emitting it so that the light behaves as if there was no object. Since the medium is symmetrical, it does not matter where the source and receivers are.

For a true cloak to work will require a really neat feat of engineering because the refractive properties of the material must be constantly adjusting with the movement of the cloak.

Group vs. Phase Velocity

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

Original site of the researchers...

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

Camera lenses

I would see an immediate use (presuming reasonable cost) in using something like this in camera lenses to combat chromatic aberration. Regular lenses bend light differently at different wavelengths so that the various colors don't focus exactly. With something that has a negative refractive index, the light could be passed through a set of these lenses to get the focal point to a single point.

Re:Camera lenses

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:Negative or less than one?

We're always looking for ways to make light go faster than C.

Write it in Java.

Re:Negative or less than one?

No, he said _faster_

Re:Negative or less than one?

So light goes backwards in this doodad?

Nope. Neither does light does not move faster than the speed of light, just phase groups. These crests and troughs of the light are features of the wave, but not any sort of signal or material in and of themselves. It's just an abstraction. Think of it this way: if you had two people a light-year apart, and they both raised their hands into the air at the same time to do The Wave, would you say that they sent a signal faster than the speed of light? If you had a one-light-year-long string of lights, and you rigged them all so they turned on at the exact same moment (presumably using some sort of countdown), would you say they've sent a signal faster than the speed of light? (Have you, in fact, sent a signal with infinite speed?) No, you haven't. You've gotten an abstraction to move faster than the speed of light, but that's not really very interesting for physics.

Re:Negative or less than one?

> Come on doofus, C is the the speed of light. How can light go faster than itself ???

Perhaps it could go as fast as his post went over your head.

Wikipedia

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:Can someone explain a refraction index?

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:Can someone explain a refraction index?

If I check another site, I lose my excuse for bashing the poor quality of the article. That's just not an option.

Re:Why do Germans seem ...

It's the beer.

Re:obligatory

It's based upon an episode of The Simpsons.

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