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A Path To Perfect Lenses?
Johan writes: "The Economist is reporting that a British scientist has invented a way to make perfect lenses. Previously, the smallest feature a lens could resolve has been limited by half the wavelength of the radiation used (for light this is in the millionths of a metre range ... very small but not good enough for many applications). With perfect lenses, this limit has been eliminated."
Doesn't the Uncertainty Principle still apply?
One form of Heisenberg's Uncertainlty principle is that if you're making measurements of both the momentum and position on an object, then the error in your measurements will obey
\delta p * \delta x >= \hbar / 4
But no-one's making measurements of momentum when they're looking through a lens, so \delta x can be made as small as you like.
:wq
perfect lenses? the elderly in Florida could use some lenses, that ballot was trickery!
It's a good thing you didn't read the part in the article where they said a negative refractive index had been achieved for certain wavelengths, otherwise your carefully-constructed artificial universe might have come crashing down around you.
Mod down posts with a "Free Mac Mini/iPod" sig, they're spam!
My God man! You're talking about X-Ray Specs!
(insert sound of every geeks' head exploding as their childhood dreams are fulfilled)
In general, Slashdot has a tendency to post a lot of science articles without sufficient context, and when you find out what's really going on, it's just pathetic.Once again, we have a large number of Slashdotters wasting their time speculating about a short article in an online publication that doesn't even specialize in science, and doesn't have any outgoing links to more detailed information. If someone submitted something to Slashdot on a computer topic with this little context or linkage to detailed info, it would get rejected.
As far as photolithography, there are plenty of theoretical methods for making small circuits: e.g. use shorter wavelengths of light, or use mechanical methods rather than optical ones (such as dragging atoms around with a device like the stylus of an STM microscope). Adding one more theoretical method is no reason to think that Intel is actually going to build the thing tomorrow.
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I checked my physics book. I was right about the definition of the refractive index. However, I was wrong about which speed it uses. In fact it is based on the phase velocity, not on the group velocity of the wave packet. The phase velocity can be grater than the speed of light without braking relativity, so in fact a negative refractive index is theoretically possible, for wavelengths which are very strongly absorbed in the material we are considering. That is how apparently some materials can have negative index for certain very specific absorption wavelengths.
s/speed/phase velocity/. The "Phase velocity" is not a speed, nor is it the speed of light. In the ionosphere, for example, the phase velocity of some radiation is greaterthan c. This does not mean that information is transmitted faster then the speed of light, or that particles move faster then the speed of light.
Speed by definition is a scalar quantity that cannot be negative.
No, a velocity can indeed be negative. I can start walking west and ask you, "with what velocity am I moving east?" The answer is negative.
So it is physically impossible to have a negative refractive index. This guy is a moron.
You have only shown that by your definition of a refractive index, which was wrong, there cannot be a negitive refractive index. It's not a physical argument at all, it's a mathematical argument that started with the wrong definitions.. And as such, is worthless.
If a light wave in vacuum is incident (at right angles) to a sheet of some substance, and within the substance there is a light wave travelling at some velocity (in the opposite direction) to meet the incident light wave, and Maxwell's field equations are satisfied everywhere, then the material has a negative index of refraction. There is nothing intrinsic in Maxwell's equations or any other known physical laws that would prevent this from happening.
Indices of refraction whith are less than one or negative are discussed in any decent wave mechanics text (Berkely Physics Course, Vol. 3: Waves by Crawford, for example.) The man the article describesd did not originate the idea of a negative index of refraction, as that possibility is inherent in the definition of hte index. He has only shown that if such a material exists (and as the article said, there are materials whcih have negative indices of refraction for microwaves and radio waves) then it could be put to some interesting uses. "Moron" indeed.
I have a positive modifier on Troll. When I mod someone Troll their karma should go UP!
Oops! You are correct. It's been about 10 years since my last optics class, and my memory was faulty (must remember to upgrate to ECC...) I thought for SURE that I remembered the refractive index being the square root of the ratios of the speeds. Thanks for the correction.
However, what gets me about the post to which I was originally responding was the guy's insistance that "this cannot be" when items in several respected science journals had reported items with refractive indixes less than zero, and even stranger items with negative mu and/or epsilon. He obviously never asked himself, "if a material has a negative mu or epsilon, what does that imply about c in the material?"
I'm fighting off a cold right now, so I'm not running on all eight cylinders. Is c=sqrt(mu*epsilon), or is it sqrt(1/mu*epsilon)? I've been pushing bits rather than EMF for too long...
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I read all about this a month or two ago, and the catch is that it has an incredibly short focal length. Specifically, the focal length is just the thickness of the lens. This is not your ordinary lens, and really can only be used for near field work. Actually the total distance between the object and the image is twice the thickness of the lens.
Anyhow, so it isn't too practical for most of the things we use lenses for, although it is still a very impressive piece of work.
I thought the resolving capability (as a function of wavelength of light used) was a limitation imposed by Quantum Mechanics. I.e. some kind of heisenberg limitation on the position of the photon when it reflects of the objects you're trying to resolve. I didn't think it had anything to do with the quality of the lens, although that would certainly limit resolution considerably further. Anyone care to comment and enlighten me?
They made the coefficient of friction between the tread and the road greater than 1, sure. But they forgot to do the same between the tread and the tire. As a result, road friction rips the tread right off the tire.
:-)
I wonder if this technology already was well developed in classified form when President Reagan proposed the Strategic Defense Initiative. It sounds like an idea people have been contemplating for a while.
...can it be done in *about an hour*?
Nah. Turns out others have noted that the story doesn't cover stuff for visible light. Guess geeks are damned to make failures like this all the time, eh? =) [Thank God for good genetics--I have better than 20:20 vision.]
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I know that no such negative index materials exists for optical wavelengths, but if it did, would this improve the resolution of lithography techniques used to etch chips? Or are the limitations in lithography due to diffraction effects with the chip masks?
-josh
Photons are an abstraction that only applies to far field radiation. The whole point is that the new technique is near-field optics.
This is an oversimplification, though it's still useful for rough estimates.
The versions I've heard - which deal with diffraction of light when passing through an aperture - almost certainly still hold. They're as follows:
The spot size to which light may be focused in a beam converging with a given angle - and by symmetry, the smallest spot that may be accurately resolved with the same lens or mirror system - is simply the aperture size that would cause light passing through it to diffract out at the angle in question. This imposes a limit of about one wavelength to feature size (give or take).
Your lens is presumably of finite size. This means that light passing through it will have some angular spreading due to diffraction, no matter how the lens works. This will cause uncertainties in where any given photon passing through the lens came from, which makes your object look blurry with the cumulative effect of all of the photons being received. Thus, for a lens of a given size and focal length, you have a limit to the feature size you can resolve.
For most cases, the two rules work out equivalently. The only exception I can think of would be a "lens" that was a curved surface enveloping the target, and even then you'd have diffraction limits to what happened to light that passed outside the lens. This is mainly an artifact of the way I stated the above rules, as opposed to any kind of breakdown.
Now, the paper's claims. Reading the abstract posted by another user, it looks like it *just might* be legit, as opposed to a math error in the calculations somewhere. It relies on funky analysis of EM propagation in the (spatial) frequency domain, which is mostly beyond my knowledge, but *might* turn out a result like this under the right conditions. However, it's triggering all of my "it turns out this doesn't happen" alarms.
Even if the assertation is correct, you'd still have things like the aperture size problem to deal with (using a bigger device doesn't help - it or at least parts of it are farther away from the subject, and distance and angular resolution scale at the same rate).
You're right, I was wrong. I checked (before you had posted) the definition and the refractive index defined with phase velocity, not group velocity (group velocity being the speed of light). So it is possible to have negative refractive index if the phase velocity is higher than c in the material.
There are materials with an index of n = -1 in the visible: metals will have an index of -1 for a particular frequency (not a range, just one). For instance, silver has an index of -1 for a wavelength of 350 nm and that is precisely the case that is discussed at the end of the article in PRL. However, to get a perfect lens the author shows that you also need a magnetic constant mu of -1. This is not the case of silver but he shows that you can still get a perfect lens as long as you stay in the near field (i.e. very close to the lens). That's why the object is only a few nanometers away from the silver lens. For photolithograhy applications, this could actually be practical.
The GHz lens made of wires and loops would be a perfect lens because they could manage to get n = -1 as well as mu = -1. By the way, the negative index for the GHz wave is achieved by stacking wires in a certain structure that is the exact analog of photonic crystals. Those are also possible in the visible. Pendry studies those too...
Mon dieu! An apology, on Slashdot! Taco, we need a new entry in the hall of fame!
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"Similarly, Maxwell's equations further suggest that lenses that would normally disperse electromagnetic radiation would instead focus it within this composite material. This is because Snell's law, which describes the angle of refraction caused by the change in velocity of light and other waves through lenses, water and other types of ordinary material, is expected to be exactly opposite within this composite. "
Two words : Transparent Aluminum
Maybe they can make my glasses zoom in on things now. I've always wanted to just look at something and see its molecular makeup =)
I am !amused.
God I hope so! What's up with some of these people using "" this was lifted right from the page source of the article. Why the hell would anyone specify -1 font size?!?!?!?!
"Listen: We are here on Earth to fart around. Don't let anybody tell you any different!" - Kurt Vonnegut
Reading the article, you'll find that the lens must be made of a material with a highly unusual refractive index of -1.
NO SUCH MATERIAL IS KNOWN TO EXIST FOR VISIBLE LIGHT ENERGY.
The article is dealing with energy in the microwave frequency range. It may help you design a better MRI (magnetic resonance imaging) device, but it will not improve your vision.
[
I mean that an image formed - whether by a lens or by any other imaging device - depends on both the location of the impinging radiation and the direction in which it is traveling. In wave terms, both amplitude and phase matter to the image, which is therefore an observation of both.
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So far, scientists at UCSD have developed ways to use this idea to focus microwaves in an MRI machine. Although those waves are in the 1 meter range, this method allows them to be more accurately focused on smaller areas. X-rays have also been observed with this method. However, visible light has not yet, and probably won't for a while.
The reason that this method is so valuable is because it removes distortion and allows precision optics to bypass a physical limit that has been hampering us for years. We'll see how quickly chip makers and others can capitalize on this technology to make better circuits.
Does this mean I will finally be able to read the horribly small fonts in some of the stories that Slashdot links to? :-)
Really. Nothing has 'been elimenated'. There is still no such thing as a 'perfect lens' and nobody is planning on building one, even in the remote future.
To quote the article 'no known materials have the refractive properties we need'.
it's all simply theory.. stating that IF such a material existed, we could make a perfect lens.
This is theoretically of great importance to photolithography, which suggests there will be lots of research into developing "perfect lenses". A perfect lens for extreme UV or x-rays would allow us to go to much smaller fractions-of-microns sizes...
There's no "we" in team, only "me"
The article did not mention it, but would this have implications for lithography, such as being able to expose a resist with very fine features, without using exotic technologies like X-rays?
I wrote parts of this stuff
At present there is just the theory to make such "superlenses". No such lenses have actually been built.
In principle, superlenses can be made for most any electromagnetic radiation. In practice, finding materials with the right refractive index is going to be difficult. So far, there seem to be materials that will properly handle microwaves, radiowaves, and maybe visible light. The authors have this to say:
Oh yeah, a slight correction--the orginial post claimed visible light was in the millionths of a meter range. Roughly speaking, visible light is about 200 to 800 nanometers--a fraction of a micron, not several microns.
As the article states, no known material with a negative refraction index exists for the optical range. Au contraire. No solid material exists, but there is one liquid.
Beer.
And they already have lenses made of beer that you can try on TODAY. All you need to do is go down to your local pub, drink a good, oh, I dunno, 7 or 8 beers (varies depending on body weight, height, experience with such lenses, etc.) and then look around. You'll notice that everything seems just a little bit clearer; not just clearer, but better. Women (or men), who you couldn't make out before because the distortion caused by normal light activity rendered them hideous, are now showing their true features: beauty, sexuality, interest in YOU.
Beer 'goggles' (as these lense instruments are affectionately known, although heavens knows why; you can't even see them) don't just make your vision clearer, either. They make everything clearer and better: thought, sexual ability, golf scores, you name it! And the great thing is, beer has been used for millenia, so you know that any potentially damaging side effects[1] have already been worked out.
So don't believe the rubbish you read in the papers. Get your perfect lenses today at your local bar or pub[2]!
[1] Some people may have adverse reactions to beer including nausea, vomiting, dehydration, a condition known as 'hangover', decreased sexual ability, loss of vocal restraint, diarrhea, and social retardation. This is not beer's fault. It's the people's fault.
[2] Beer should not be consumed by pregnant women, people with heart conditions, people on heroin, cocaine, Tylenol, or any number of other drugs, or alcoholics currently enrolled in court-ordered rehabilitation program.
Forming an image (using a lens or mirror or any other electromagnetic sensor) is not just a measurment of the position of impinging photons, but also of the direction from which it came. This is where momentum - a vector quantity encompassing both mass and velocity - comes into play. Thus the uncertainty principle is in fact the source of current thinking of the fundamental limits of imaging systems.
The interesting part of the article is the possiblity of systems in which the constraints of the uncertainty principle might be relaxed
A negative refractive index for a MATERIAL would mean negative speed of light in the material by definition. What they have is not a material, but is lens made of "wires and rings". Therefore it is not fair to say that it has a refractive index as such. I can for example put a mirror in water and by tilting it just right I can deflect incoming light rays in the direction equivalent to index of -1. But this does not mean water is a perfect lens. I agree that such a technique might help with the diffraction problem, I just disagree with saying that the thing has a negative refractive index, because of the definition refractive index being what it is.
I can't wait to see what Hubble produces if/when this technology is applied to the lenses in it.
I'm not quite sure where the momentum is being measured (unless it's a colour photographic plate measuring frequency). Do you mean the that at the lens the refraction (depending on the angle of incidence) constitutes a measurement? I'm not so sure it does.
:wq
Actually, sir, the refractive index of a material is the square root of the ratio of the speed of light in in a vacuum vs. the speed of light in the material. Therefor, a negative refractive index is perfectly valid. Go look it up in a good bood on physics.
Furthurmore, I almost gave you an "overrated" myself, before deciding to post instead. The moderator probably used "overrated" since there is no "-1: false" moderation. Your post isn't flamebait (although some of your responses border on flamebait), nor is it a troll, it is simply wrong.
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1. Photonic band gap materials. Prof. Pendry has written several papers on this subject so I imagine this negative index work is related, i.e., it would be realized as some sort of photonic band structure material. You can think of photonic band gap materials as 3-dimensional diffraction gratings. In theory, such a material could "trap" a photon, reducing its velocity to zero.
2. Near field optics. In one incarnation, the near field microscope uses a sharp AFM tip which focuses light (which is an oscillating EM field) like how a lightning rod focuses static electric fields. The resolution of this microscope is a few nanometers or perhaps sub-nanometer. This surpasses the "diffraction barrier" by better than a factor of one hundred.
the story doesn't cover stuff for visible light.
But it DOES note that you can make something like it for microwaves - out of conductive rings and wires.
Now the only difference between microwaves and visible light is the wavelengh. Microwave plumbing tends to have segments measured in quarter wavelengths and larger - and visible light is moderately large compared to reasonably sized molecules.
So it seems to me you OUGHT to be able to make your rings and wires with nanotech. Maybe buckytubes for the wires and cyclo--ene or another buckystrucure for the rings. And as with any nanotech construct it would tend to be either perfect or massively broken.
You might get your perfect optical lenses after all - at least for one color of light at a time...
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http://www.sst.ph.ic.ac.uk/photonics/abstracts/ne
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The article says that Dr Pendry has theorized that material with negative refractive index could make a perfect lens, but it hasn't been done. Materials having a negative refractive index do exist for microwaves and radio waves but no-one's made a perfect lens from them. Also there is, as yet, no know material with a negative refractive index for visible light. Thus, so far, they've pretty much not invented anything. The article's not quite as positive as the /. blurb.
Remember the recent findings of materials that change the handedness of em? I.e. left-handed instead of right-handed, negative dielectric constant. This URL talks about it:
i brary/PR/2000/blucsd1.htm?terms=negative+d ielectric+constant
http://composite.about.com/industry/composite/l
Here's a key excerpt:
"Similarly, Maxwell's equations further suggest that lenses that would normally disperse electromagnetic radiation would instead focus it within this composite material. This is because Snell's law, which describes the angle of refraction caused by the change in velocity of light and other waves through lenses, water and other types of ordinary material, is expected to be exactly opposite within this composite. "
Now I'm not physicist, but this sounds like exactly what would be needed.
glasnost
The article mentions applications of this lense technology in wavelengths outside the visual spectrum, eg. radio and microwaves, toward medical devices. Could this be applied to data communications as well? Seems like wireless folks would be interested in taking this technology beyond the theoretical realm.
"My mother works for Microsoft now. A whole other cult."
According to the paper, the object and image are 80 nm from each other. That's pretty darn small.
To actually use these lenses, then, you'd have to keep the object and lens from moving toward or away from each other even a fraction of a nanometer.
If you could overcome the problems, this would be great for nanotech.
P.S. It might work with copper and gold too.
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The camera by, I think it was Sony, that when set into infrared light mode during daylight, would see through soft clothing? I wonder if it would be possible to create an infrared amplifying lense (with a reactive substance to convert it to the normal spectrum) in order to give human infrared vision without electronics.
I always thought that the resolution limits for a given wavelength were beacuse of the "effective size" of the photon. For example, a 150MHz photon could only resolve features larger than about 2 meters, it's wavelength.
This would require receptors of infrared light in the retina. Night-vision devices convert IR into the visible spectrum (usually puke green) so you can see it. Unless you can come up with IR cones or rods for the human retina, you'll probably just end up with a burning sensation. That'll be your wallet after purchasing the lens. ;)
I think it's called _glass_!
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Remember the experiment where electrons where shot through holes, and they would interfere with each other, even though there was only one electron in at a time? People have tried to observe the electron, but when using fotons with a big wavelength the beam was too imprecise, and when using fotons with a small wavelength the interference was annihilated.
I'm not exactly sure, but those lenses might be used to concentrate fotons with a big wavelength, so that the beam is precise enough AND doesn't interfere!
You don't get the point, do you, you moron?
Glass lets the light through. This substance reflects light into itself, to emerge on the other side. Not the same thing.
Any technology which is distinguishable from magic is not sufficiently advanced.
Doesn't the Uncertainty Principle still apply?
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.