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New Flat Lens Focuses Without Distortion
yahyamf writes "Applied physicists at Harvard have created an ultrathin, flat lens that focuses light without the distortions of conventional lenses. 'Our flat lens opens up a new type of technology,' says principal investigator Federico Capasso. 'We're presenting a new way of making lenses. Instead of creating phase delays as light propagates through the thickness of the material, you can create an instantaneous phase shift right at the surface of the lens. It's extremely exciting.'" And by "ultrathin," they mean it — 60 nanometers thin. The big advantage for this technology, aimed at telecommunications signals, is that "the flat lens eliminates optical aberrations such as the 'fish-eye' effect that results from conventional wide-angle lenses. Astigmatism and coma aberrations also do not occur with the flat lens, so the resulting image or signal is completely accurate and does not require any complex corrective techniques."
Will is make my ass look big?
Does this mean that very large refractive telescopes will make sense again? If we sandwich a few of these with the metasurfaces tuned right, could we build a telescope that is a slab instead of a tube? How about telephoto lenses built into camera phones? Or cheaper orbital telescopes?
I wonder if this would work with glasses.
Look at pin hole cameras. They actually lack lenses but focus to infinity. The trick is to filter out the incidental indirect rays that cause the blurring. The downside with pin holes is they only allow in a small amount of light. I'd love to see a fast lenses, something below F2.8 that doesn't require focusing.
I cannot wait to see this applied to new camera lens so I can have even better image quality.
But how to fix its probable fragility?
That's really all that matters these days. Everything else can be easily corrected in software. Chromatic aberrations are more difficult to deal with nicely.
-Matt
All signals are communications signals.
according to this report it's not a lens, but a diffraction grating.
From linked article:
"Our flat lens opens up a new type of technology. We're presenting a new way of making lenses. It's extremely exciting," says principal investigator Federico Capasso, professor of applied physics at the Harvard School of Engineering and Applied Sciences (SEAS).
Sorry, matey, it ain't that new, it's just a new application of a well established physical property. I do seem to remember using diffraction gratings to magnify light-bending effects at college in 1992 - specifically to fire an EM pulse at 450nm (near blue part of the visible spectrum) through a sample and use a calibrated* diffraction grating to amplify the signal to a photographic plate. What you end up with, essentially, is a highly magnified image (on the order of millions of times) with a very low distortion, with which you can determine the structure of the sample (be it a crystal lattice, eg. graphite, or a double helix, eg. DNA; each molecule has its own unique diffraction pattern). Generally you would use X-rays as pretty much anything is at least partially transparent to this wavelength, but since we had to use visible light from a very low powered lasing LED, we had to use visible-transparent samples. We got stuck with a quartz crystal. Still interesting physics, though, and some very pretty pictures.
*calibrating a diffraction grating is very simple: all you do is make the spacing between the lines on the plate equal to the wavelength of the light you're using. For far blue, you'd use a 400nm grating, for red 700nm. These are but two of several calibrated plates available.
Operation Guillotine is in effect.
If we sandwich a few of these with the metasurfaces tuned right, could we build a telescope that is a slab instead of a tube?
Only in limited cases, because it's only applicable from near-infrared to terahertz frequencies. UV and visible band are pretty much all out from the sounds of it.
Also: the lens is very thin. Nothing else is - just the lens. Ie, the objective or sensor still has to be some distance behind it, and I'm sure there are limitations with respect to angles. So you still need a tube - especially if the lens is very large in diameter.
This is fascinating, because it sounds like it is operating as a phased array; they *delay* the light depending on where it strikes on the lens. Wild! Phased arrays work by delaying the signal, thus steering the electromagnetic wave, but that's when you're generating or receiving...not modifying and retransmitting!
However, they're doing it in this case by physical manipulation of the gold/silicon structures at construction time. It's not tuneable afterward.
That's fine for telecom / fiber applications, where you only have a fixed number of specific wavelengths. However, astronomers might not mind being restricted to imaging just that one wavelength or that high in the light spectrum.
Sadly, this limitation also makes it useless for semiconductor lithography, which is UV to x-ray range.
Please help metamoderate.
The lens is tuned to a single wavelength of light and was demonstrated with a laser.
It's not apochromatic and not instantly useful to most lensing applications.
The authors say that it could potentially be, in the future. But that often means "give us more funding."
Screw glasses, what about Contact Lenses?
Or what about Intra-ocular lenses?
Or could you just implant metamaterials in your cornea to correct your vision?
?
Really? No, REALLY?
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Screw glasses, what about Contact Lenses?
I'm not sure how many people demand perfectly flat contact lenses, but it can't be many...
"There is more worth loving than we have strength to love." - Brian Jay Stanley
It remins me to the idea behind Fresnel lenses, it's a kind of 'flat' lens, they are used in lighthouses,
Fresnel lens.
but taken to nanoscale, and without aberration. Impresive.
My colleagues work on the exact same gold-based nano-antennae used by this work. All of the nano-antennae on the lens' surface are basically arranged to absorb and re-transmit the incoming light into a near perfect spot. Because it uses metal on nanoscopic scales to manipulate light in a way other than pure reflection (like a mirror), it's in the field of plasmonics. (Below a certain frequency [of light] the electrons in a metal react like a plasma, hence the name.)
Whenever us optical engineers hear about plasmonics, we internally roll our eyes, because metal almost always absorbs far too much light to be useful. Even tens of nanometers of penetration and/or propagation can extinguish almost all of the light. This essentially relegates the entire field to the realm of theoretical curiosities and nothing more. (This work uses 60nm thick gold)
The authors of this paper admit that absorption is their biggest obstacle, as this lens only passes 10% of the incoming light. There are other issues for making this work a reality, but they pale in comparison to the classic brick wall you get when passing light through metal.
AccountKiller
[NT]
File under 'M' for 'Manic ranting'
Prepare the sharks.
Hi everyone. I'm a co-author on the article, and I'd be happy to answer any questions you may have, though probably tomorrow. I'm hoping that this goes better than the last time I tried this (see here: http://slashdot.org/comments.pl?sid=1747464&cid=33185134), where no questions were asked and most of the discussion centered around mildly funny jokes. I appreciate those as much as the next person, but if anyone likes, we can discuss science =].
and I don;t mean those little lines on the globe.
I have been an amateur photographer most of my life. The holy grail of photography, for me, has been to find film or techniques that bring film images as close to the latitude of the human eye. In Film Speak the human eye can handle around 12 to 14 f-stops around a given lighted scene. Which is to say that the information that your retina takes in ( given a central point that has lighted value of n ) can be discriminated 12 to 14 f-stops darker or brighter.
We have all experienced taking a picture of a brightly or darkly lit scene. Sunsets are a great example. We as a viewer can enjoy a sunset and see all the detail ( quite clearly ) around us AND enjoy the sunset. This is one of the hardest, if not impossible, things to do with any camera, digital or otherwise for the simple reason that to correctly expose for the sky ( the sunset ) we will always drastically underexpose everything else around us by a large factor.
I think this can be solved with a digital camera, but not until computing speeds drastically increase and not just by a little bit, but by several orders of magnitude since it would mean that each individual pixel would have to be processed and recorded for the sufficient amount of time to record the detail level in a still shot. So in a Nikon D5100 the sensor has ~16 million pixels. To obtain a shutter speed of 1/125 of a second ( .008 seconds ) each pixel who have to be processed in about 5 pico seconds ( 16 million / .008 = 1 * 5 -10th) and of course faster shutter speeds, well you get the point.
Hey KID! Yeah you, get the fuck off my lawn!
Would this be useful for beam expanders in large scale IR lasers? A lot of very long range lasers need a big aperture to get around diffraction limits, and making the optics the equivalent of gossamer mirrors is a neat trick. Though how much better is this compared to photon sieves? Is it too fragil for high power IR lasers though due to heating of the gold nanoantennas?
MOD UP
Where are my modpoints when I need them?
This is good news
I'm a bit of a science hack, but could this method have implications for sound amplification?
Speaking as both a photographer and a very near-sighted person, it would be really awesome if these new lenses were also free(r) from dispersion as compared with standard lenses. (Dispersion is responsible for colour separation in a prism. It also causes orange-yellow and blue-violet fringing in simple lenses such as eyeglasses. Cameras use compound lens elements in a clunky and expensive way to address this problem - see http://en.wikipedia.org/wiki/Achromatic_lens )
Cameras would be lighter and more accurate, and eyeglasses would be lighter and thinner. Maybe this new technology would even improve contact lenses.
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Would this allow the creation of lasers that stay focused on a longer distance? This could allow easier very long range communication or even power transmission over very large distances.
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Will this help with things like google glass to display focused content closer to our eyes?
By the illustration in the article this looks like a nano-scale Fresnel lens, but because of the nano-scale "antennas" it can be tuned to a specific frequency of light. A most interesting use of an old technology. I see something like this as being extremely useful in point-to-point laser communications, say between the Earth and a Moon base.
Sticker Lenses, only on a nano level. Am I missing something?
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As someone who wears small telescopes on his face on a daily basis, can we please get this technology into eye glasses?
Sure I would still have to wear glasses, but at least they might weigh a bit less than my 1kilo "ultrathins" I currently endure.
20nm sounds great! Though they might have to buffer them up a bit so I don't cut my face or nose off or something by mistake.
Luckily we have an advanced technology that will solve the flexing problem.
It's called a sheet of glass. Sandwich your flat lens between two of them. In fact, I bet you could manufacture the nanoantennas directly on the glass.
You may incur a tiny optical loss due to reflections, but less than with a conventional lens. Also since the flat lens only works in a narrow wavelength, you can, if needed, use coatings to prevent reflections at that wavelength.
What I want to know is: what happens if you stack a bunch of flat sensors, each tuned to a different frequency, so you cover the visible spectrum? I imagine that a flat-lens blocks and/or reflects light of wavelength smaller than the nano-antennae, but how big is that effect? Would it be practical to stack these or not?
This is a smaller version of the "zone plate" (see http://en.wikipedia.org/wiki/Zone_plate). These are intrinsically designed to operate at a single frequency (i.e. light color). If you designed a lens for a single color, you could reduce its distortion, too.
Of course there's a lot of detail missing from the article, but something that has to be said is that some of those "annoying" distortions that they talk about are in fact valuable. The ideal camera is assumed to have a projective transformation and no chromatic aberration. But a true projective transform has some undesirable characteristics. For example, assuming that the photograph will eventually be shown on a flat surface, there will be a 1/r^2 drop off in intensity because the angle of light is being spread out across a larger area on the edge of the detector (providing for fewer photos/area) when compared with the center of the detector. Of course, if your detector is a spherical shell, that eliminates some of the issues. But even so, once you flatten it back out (onto film or onto your computer screen) the projective distortions at large angles from the image center will in some cases look worse than the typical thick-lens issues like fish-eye behavior.
Sometimes there just isn't enough light and you maxed out your sensitivity, the only place to get proper exposure is open up the aperture. If your camera has fixed small aperture, such as a pinhole, then you're just not going to be able to to take that picture.
That's because latitude was mostly used for film which has a fixed ISO and therefore fixed exposure point. Knowing the film's latitude (1 stop above and 2 stops below, for example) would allow you to under and over expose by that amount without losing much information, either for photographic effect or to use exposure parameters otherwise not reachable. This way you could bump ISO and compensate by longer development time (look up push/pull film processing).
With digital, all of that is done in camera and the variable ISO and histogram has made latitude less useful. Dynamic range is where it's at now.
While one can talk about plasmons going through bulk metal, the majority of research I've seen in the field of plasmonics is with surface plasmons. These are excitations of oscillations along the interface of two materials, say a plasma like oscillation on the metal side, and an RF like excitation on the insulator side. The penetration of these into the metal is on the order of the skin depth, and because they are not just simple photons bouncing along the surface, they go much further than optical absorbance would suggest. These have been used for many decades by radar and RF people by a different name: surface waves. Currently work is finding use of such processes for transport of THz waves along surfaces of wires, over many meters of distance and of much higher efficiency than trying to build tiny wave guides (and is not quite the same as just using a wire, as waves are launched onto and off of the wire.
Plasmonics has other applications beyond just testing plasmon theories. Surface enhanced Raman spectroscopy is used for doing spectroscopic work on various molecules and solid state materials, and by using plasmons can sometimes allow for spectroscopy of single molecules. This process has been around for decades now and is part of what is being used for medical tests-on-a-chip work. There are also applications in use for some forms of near field scanning optical microscopes.
Sounds like they actually invented something...
Posted from my Android phone. Oh, I can change this? There, that's better...
So... it's a Fresnel zone plate? 'Cause they had those in the eighteenth century.