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Night vision glasses: nanocrystals allow direct vision into infrared

smh.com.au

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Re: Night vision glasses: nanocrystals allow direct vision into infrared

#21

Post by jessriedel »

colanderman wrote: post #10
cthulhuology wrote: post #7

Reading the article it hints at the reality that it doesn't actually work like passive glasses as it implies. the blueshift effect happens because they're using a laser to excite the crystal and it later emits the shifted light, but you have to pump a lot of energy in for that output. Simple conservation of energy implies this won't work for normal night vision applications, instead they want to shine a laser spotlig…

> Simple conservation of energy implies this won't work for normal night vision applications Not at all. For a single photon, sure. But in aggregate many low-energy photons can charge a material to emit fewer high-energy photons. Ex. https://www.newport.com/f/near-infrared-nir-sensor-cards

Yea, in fact I think it's the second law (no entropy decrease) rather than first law (energy conservation) which is the restriction. Devices up-converting photons to higher frequencies require power input.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#22

Post by lolc »

m4x wrote: post #12
cthulhuology wrote: post #7

Reading the article it hints at the reality that it doesn't actually work like passive glasses as it implies. the blueshift effect happens because they're using a laser to excite the crystal and it later emits the shifted light, but you have to pump a lot of energy in for that output. Simple conservation of energy implies this won't work for normal night vision applications, instead they want to shine a laser spotlig…

> The crystals act as antennaes that receive a photon emitted in the infrared, combine them with a photon from a laser and then "upconvert" the combined photon to the visible spectrum. It doesn't sound like you need to illuminate the scene with a laser spotlight, it sounds like they will input a small amount of laser light into the crystal film on the glasses. The externally sourced IR photons will combine with the i…

Is there any chance that the "combined photon" will have the same direction as the original one? Otherwise there will be no image, just light.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#23

Post by dosshell »

Did they take the biggest night googles available for the "traditional" picture?

Those I have used from the military where much much smaller (but they did not have autofocus).

I agree with some of the comments here: that it is misleading that they are not passive and that no prototype exist.

Even if it is a good idea I would never invest in a company which is not always totally honest, even in headings and pictures.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#24

Post by tlb »

kneel wrote: post #14

These night vision glasses don't exist and the use of the phrase 'allow direct vision' is misleading seeing as they're using high powered lasers to see the blue shift. This lab has only made a nanocrystal that might enable this technology one day. The fact that everyone in the linked video is wearing funny looking green glasses is misleading, those are just safety glasses. These types of news blips are depressingly c…

Also, it wouldn't preserve the direction of photons. So you couldn't just put a sheet of something in front of your eyes, you'd have to have a lens to focus the incoming image on a screen, and another lens for your eyes to focus on the screen.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#25

Post by smaddox »

zokier wrote: post #15

I'd point out that night-vision and IR vision can (and even maybe should) be considered distinct, even though admittedly they are widely mixed up in common parlance. But especially in military night vision devices are usually based on the principle of image intensification, i.e. amplifying the light in visible spectrum, instead of IR imaging.

Not quite, since night vision goggles also amplify near IR light, which is much more abundant at night than visible light (e.g. starlight). Also, they can be coupled with IR LEDs or bulbs in order to gain a tactical advantage over an enemy without night vision.

That being said, night vision and thermal vision are distinct.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#26

Post by hinkley »

jessriedel wrote: post #21
colanderman wrote: post #10

Earlier quoted context omitted.

> Simple conservation of energy implies this won't work for normal night vision applications Not at all. For a single photon, sure. But in aggregate many low-energy photons can charge a material to emit fewer high-energy photons. Ex. https://www.newport.com/f/near-infrared-nir-sensor-cards

Yea, in fact I think it's the second law (no entropy decrease) rather than first law (energy conservation) which is the restriction. Devices up-converting photons to higher frequencies require power input.

But you can turn three infrared photons into a single red photon, if the energy levels add up.

That would, for instance, allow you to make safety goggles for detecting hot spots. Could be useful for firefighters or factory workers.

The problem with a passive device would be that if you walked past something hot enough your goggles would white out (well, red out), and you might be effectively blind. At least with the passive device you can turn it off briefly so you can see where you're going.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#27

Post by jessriedel »

hinkley wrote: post #26
jessriedel wrote: post #21

Earlier quoted context omitted.

Yea, in fact I think it's the second law (no entropy decrease) rather than first law (energy conservation) which is the restriction. Devices up-converting photons to higher frequencies require power input.

But you can turn three infrared photons into a single red photon, if the energy levels add up. That would, for instance, allow you to make safety goggles for detecting hot spots. Could be useful for firefighters or factory workers. The problem with a passive device would be that if you walked past something hot enough your goggles would white out (well, red out), and you might be effectively blind. At least with the…

> But you can turn three infrared photons into a single red photon, if the energy levels add up.

You can't do this with a passive device, because the single visible photon has less total entropy than the three infrared photons. Yes, it satisfies the first law of thermo, but it violates the second.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#28

Post by colanderman »

jessriedel wrote: post #27
hinkley wrote: post #26

Earlier quoted context omitted.

But you can turn three infrared photons into a single red photon, if the energy levels add up. That would, for instance, allow you to make safety goggles for detecting hot spots. Could be useful for firefighters or factory workers. The problem with a passive device would be that if you walked past something hot enough your goggles would white out (well, red out), and you might be effectively blind. At least with the…

> But you can turn three infrared photons into a single red photon, if the energy levels add up. You can't do this with a passive device, because the single visible photon has less total entropy than the three infrared photons. Yes, it satisfies the first law of thermo, but it violates the second.

You absolutely can, there are existing products that do exactly this. See the link in my post.

Re: Night vision glasses: nanocrystals allow direct vision into infrared

#29

Post by jessriedel »

colanderman wrote: post #28
jessriedel wrote: post #27

Earlier quoted context omitted.

> But you can turn three infrared photons into a single red photon, if the energy levels add up. You can't do this with a passive device, because the single visible photon has less total entropy than the three infrared photons. Yes, it satisfies the first law of thermo, but it violates the second.

You absolutely can, there are existing products that do exactly this. See the link in my post.

Thanks for emphasizing this, and I agree I need to qualify my statement. I haven't completely understood the restrictions yet, but the effectiveness of this device has to be conditional on the fact that the IR laser is a laser, or otherwise is in some low-entropy coherent state. Otherwise, it could be used to transform part of a uniform IR bath into high-frequency photons, passively generating a temperature gradient from nothing.

The incoherent case is the relevant situation when you're talking about passive glasses for viewing a scene in ambient IR light.

Here's one place where this is mentioned:

http://physics.stackexchange.com/questions/98790/what-low-le...

Still looking for an authoritative treatment...

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