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from the but-don't-look-into-the-light dept.
Night vision goggles do a great job of countering the human eye's poor ability to see in the dark, but the devices are usually bulky, requiring several layers of lenses and plenty of power. But thanks to research from the Australian National University (ANU), a new type of nanocrystal could grant night vision powers to a standard pair of specs, without adding any weight.
Darkness, as we perceive it, is the absence of light on the visible spectrum that our eyes can detect, but there's still plenty of light at other frequencies that we can't use. Night vision goggles make use of the near-infrared spectrum, and convert the photons from that light into electrons that light up a phosphor screen inside the device to create the image. But all that makes for a chunky, power-hungry device.
The ANU team's nanocrystal can be used to create night vision devices that forgo electricity completely, by converting incoming photons from infrared light into other photons on the visible spectrum, to allow the human eye to see in the dark.
(Score: 3, Interesting) by dlb on Thursday December 08 2016, @06:12PM
However as the lead author of the study implied in the article, embedding millions of these nanocrystals inito a thin film on a pair of glasses would open up a wide swath of invisible frequencies, including "near-infrared illumination," to our vision. Think of all the invisible EMR bouncing around out there. If so, then the glasses wouldn't need additional energy.
Either way, wearing a pair of those glasses at night, or even during the day, is going to be an experience I'd love to have.
(Score: 0) by Anonymous Coward on Friday December 09 2016, @03:56AM
Either way, wearing a pair of those glasses at night, or even during the day, is going to be an experience I'd love to have.
Replying back-to-front, I absolutely agree -- the abiity to have full color vision at frequencies one, two, or three (or more? but losses multiply, so I'm afraid not) octaves down from visible wavelength would be fascinating. I'm not sure this is the most practical realization of such IR-seeing goggles, but it's absolutely a cool idea.
embedding millions of these nanocrystals inito a thin film on a pair of glasses would open up a wide swath of invisible frequencies, including "near-infrared illumination," to our vision. Think of all the invisible EMR bouncing around out there. If so, then the glasses wouldn't need additional energy.
But it doesn't open a wide swath -- if you absorb two photons, and reemit one photon with half the wavelength, you're basically just shifting the human eye's 400-750 THz (750-400nm) range down an octave to 200-375 THz (1500-800nm). (While you should be able to stack them in series to go two or three octaves down, it's not clear whether you can do this in a way that, as Immerman suggests, would add all those bands together. For now, let's just consider a single-octave filter.)
We can consider this in two ways -- I find frequency easier for this particular problem, as that graph is better-behaved in the region of interest, but wavelength is more commonly used, and of course they'll both yield the same answer.
The discrepancy, of course, is due to the different types of spectral density -- it's analogous to the difference between a world map using Mercator vs. Gall-Peters projections.
So now all we need is a spectrum of our light source. While we're not likely to use sunlight directly, starlight is basically comparable (despite some stars being redder and some bluer), and moonlight is simply reflected sunlight, so it's a decent first approximation, and it's easy to get data on. Here's a nice page with both graphs shown [sciencequestionswithsurprisinganswers.org] -- though that refers to sunlight in space, or as it enters the atmosphere; I couldn't quickly find a similar pair of graphs with atmospheric absorption included, but NIR is attenuated more than visible. I think you'll agree, using either method with the corresponding graph, that the power in the NIR band is not quite enough to break even. (Though as Immerman points out, if these add to, rather than obscuring, visible light, that may still be helpful.)
Airglow, for what it's worth, is much higher in NIR than visible -- not sure that's enough to make this viable, since it's very dim in the visible, but it's an interesting angle I hadn't considered.
However, if we're talking about stray light generated on or near Earth's surface (e.g. skyglow from a nearby city or highway), we have to consider two types of light. First, we have blackbody radiation -- whether from a fire or an incandescent lamp, this will tend to be comparatively cool, and have less visible light; in fact, these light sources should do much better than break even. On the other hand, we have LEDs, fluorescent lights, discharge lamps of various sorts, etc. -- these all have non-blackbody spectra selected or designed to provide visible light, and thus very likely to have little NIR content. (The rather bright sodium line at 819nm might seem like a counterexample, but of course that ends up at a barely-visible 410nm.) I believe these non-blackbody sources, taken together, already dominate generic city skyglow and lighted highways, and with the growth of LED and HID headlights, even unlit highways are trending this way.
(Score: 2) by Foobar Bazbot on Friday December 09 2016, @03:57AM
That was me; accidentally ACed it.