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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."
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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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!
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).
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...
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? :-)
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:
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.
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 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.