Slashdot Mirror
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?
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.
Sometimes you want to focus on the tits and blur everything else...
Either I'm taking you too literally, or you're doing it wrong.
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
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 =].
Best explanation I have found that says it succinctly. I hope it helps.
Dynamic range = difference between highest and lowest(brightest/darkest) value that can be recorded on a medium.
Latitude = The degree of variation allowed above or below a certain setting, derived directly from dynamic range. i.e latitude a film is for a certain exposure, how many stops of headroom it has above and below before you lose details.
And just for fun...
Contrast = the difference between intermediate tonal values within a certain range. Generally, contrast is inversely related to dynamic range. A wider range allows finer graduations and hence lower contrast if desired. Contrast is directly related to the tonal response of the medium and can be visualized as a curve from light to dark. The steeper gradient of the curve, the higher the contrast at that point.
Hey KID! Yeah you, get the fuck off my lawn!