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Material With Negative Refractive Index Created
Posted by
kdawson
on Mon Dec 18, 2006 03:57 PM
from the seeing-right-through-it dept.
from the seeing-right-through-it dept.
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."
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Scientists Make Item Invisible to Microwaves 219 comments
Vicissidude writes "A team of American and British researchers has made a cloak of invisibility. In their experiment the scientists used microwaves to try and detect a copper cylinder. Like light and radar waves, microwaves bounce off objects making them visible and creating a shadow, though it has to be detected with instruments. If you can hide something from microwaves, you can hide it from radar and visible light. In effect the device, made of metamaterials — engineered mixtures of metal and circuit board materials, which could include ceramic, Teflon or fiber composite materials — channels the microwaves around the object being hidden. When water flows around a rock, co-author David R. Smith explained, the water recombines after it passes the rock and people looking at the water downstream would never know it had passed a rock. The first working cloak was in only two dimensions and did cast a small shadow, Smith acknowledged. The next step is to go for three dimensions and to eliminate any shadow."
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A Step Toward an Invisibility Cloak 197 comments
Technology Review has a writeup on the latest advance in the lab towards an invisibility cloak made of metamaterials, described this week in Science. We've been following this technology since the beginning. The breakthrough is software that lets researchers design materials that are both low-loss and wideband. "The cloak that the researchers built works with wavelengths of light ranging from about 1 to 18 gigahertz — a swath as broad as the visible spectrum. No one has yet made a cloaking device that works in the visible spectrum, and those metamaterials that have been fabricated tend to work only with narrow bands of light. But a cloak that made an object invisible to light of only one color would not be of much use. Similarly, a cloaking device can't afford to be lossy: if it lets just a little bit of light reflect off the object it's supposed to cloak, it's no longer effective. The cloak that Smith built is very low loss, successfully rerouting almost all the light that hits it."
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It's good news ... (Score:3, Funny)
Re:Why do Germans seem ... (Score:5, Funny)
Parent
Free University (Score:3, Informative)
Re: (Score:3, Insightful)
Re:Why do Germans seem ... (Score:4, Insightful)
Three points...
1. Not only won't it happen, it CAN'T happen. IQ tests are culturally biased. Comparing different cultures by measuring IQs has to many uncontrolled variables to provide meaningful results.
2. IQ test don't measure anyting other than ability to take IQ tests.
3. Don't make the mistake of thinking that just because something is politically incorrect it isn't also morally or ethically incorrect, or just plain vile and wrong.
Parent
yes, but RTFA, they were not first. (Score:4, Informative)
Re:yes, but RTFA, they were not first. (Score:5, Informative)
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Re:yes, but RTFA, they were not first. (Score:5, Funny)
Parent
Re:yes, but RTFA, they were not first. (Score:5, Funny)
Parent
Visible spectrum and cones (Score:5, Informative)
Parent
Re:Visible spectrum and cones (Score:5, Funny)
Parent
Tetrachromats need not apply (Score:3, Interesting)
Re: (Score:3, Informative)
http://science.slashdot.org/article.pl?sid=05/04/
does this mean? (Score:3, Interesting)
--josh
obligatory (Score:3, Funny)
Re:obligatory (Score:5, Informative)
http://en.wikipedia.org/wiki/Overlord_meme [wikipedia.org]
Parent
Re:obligatory (Score:4, Funny)
Parent
Re: (Score:3, Funny)
-nB
This will revolutionize... (Score:4, Funny)
All right! (Score:5, Funny)
Finally... (Score:5, Funny)
For the first time, I may have a real shot at seeing real life naked boobies
Re: (Score:3, Funny)
Have you tried just looking down?
This should come in handy... (Score:4, Funny)
Invisibility cloak? (Score:5, Insightful)
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? (Score:5, Interesting)
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.
Parent
Re: (Score:3, Funny)
Group vs. Phase Velocity (Score:5, Informative)
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: (Score:3, Interesting)
And it's important to point out that the material they're talking about has a negative phase velocity.
If you had a material with a negative group velocity, it would violate causality, because the information would get to its destination before it was transmitted. (In fact, any material with a group velocity n<1 would also violate causality, because according to special relativity, there would be a frame of reference in which the reception came after the emission.)
A few years ago, when the first news a
So the pencil bends the other way now? (Score:3, Informative)
Sheesh.
Transcript from Experiment (Score:4, Funny)
Re:Transcript from Experiment (Score:4, Funny)
Parent
What we need now: SEP fields (Score:4, Insightful)
However, what I'm really looking forward to is a Somebody Else's Problem device -- this will make all of the other foophraw unnecessary.
Original site of the researchers... (Score:5, Informative)
Camera lenses (Score:5, Interesting)
Re:Camera lenses (Score:5, Informative)
Parent
cloak of invisibility -- maybe not (Score:3, Interesting)
Re:Negative or less than one? (Score:5, Funny)
Write it in Java.
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Re:Negative or less than one? (Score:5, Funny)
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Re:Negative or less than one? (Score:5, Insightful)
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Re: (Score:3, Interesting)
Re:Negative or less than one? (Score:5, Funny)
Perhaps it could go as fast as his post went over your head.
Parent
Wikipedia (Score:5, Informative)
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Re: (Score:3, Informative)
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 a
Re:Can someone explain a refraction index? (Score:4, Funny)
Parent
Re: (Score:3, Informative)
When you have two materials with different refractive indices up against each other, light bends by some angle (the angle depe
Re: (Score:3, Informative)
Re:Can someone explain a refraction index? (Score:5, Informative)
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."
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Re:Can someone explain a refraction index? (Score:5, Funny)
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Re:Negative OK, but why |-1| ? (Score:4, Insightful)
Basically all it means is that light is going to bend opposite of what we would normally expect. Instead of bending towards the interface, light will bend away from the interface. There's no fancy u-turns or anything like that. The negative sign is purely a consequence of the convention by which we choose our cross products when it comes to the vector form of Maxwell's Equations. Normally we use a right-hand convention, but a metamaterial behaves using the left-hand convention. This negative sign is one way of achieving the same effects using the right-hand vector convention.
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Re: (Score:3, Informative)
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.