Night-vision goggles

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shpalman
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Night-vision goggles

Post by shpalman » Tue Jun 15, 2021 6:45 pm

Ultra-thin film won't actually turn regular glasses into night vision goggles for a couple of good reasons I'm about to give you

The (open-access) article is at https://doi.org/10.1117/1.AP.3.3.036002

The first issue is that unless you can turn the infra-red photons into visible photons going in exactly the same direction, all you'll do is make the film on your glasses glow diffusely. Part of the reason why night-vision goggles are bulky and heavy is that they need the optics to make it seem like the the image they've created is coming from infinity.

The second issue is that you can't just turn infra-red photons into visible photons without a source of energy, which in this technique is provided by a strong near-infrared pump beam from a high-power laser diode. Just because you can't see that doesn't mean it's a good idea to shine it anywhere near your eyes.

Alternatively you could use a strong visible-light beam and just shine it directly at whatever the f.ck you want to see.

Of course their work is useful and has applications but the night-vision goggles thing is just a pathetic bid for attention from a press release.
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Re: Night-vision goggles

Post by Boustrophedon » Tue Jun 15, 2021 8:19 pm

Nothing to do with the above paper, which I don't understand anyway: I don't understand why IR vision equipment is so expensive, given that most of the camera chips in use are quite sensitive in the near IR anyway, and have to be equipped with IR filters to correct for this.
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Re: Night-vision goggles

Post by monkey » Tue Jun 15, 2021 8:22 pm

shpalman wrote:
Tue Jun 15, 2021 6:45 pm
Ultra-thin film won't actually turn regular glasses into night vision goggles for a couple of good reasons I'm about to give you

The (open-access) article is at https://doi.org/10.1117/1.AP.3.3.036002

The first issue is that unless you can turn the infra-red photons into visible photons going in exactly the same direction, all you'll do is make the film on your glasses glow diffusely. Part of the reason why night-vision goggles are bulky and heavy is that they need the optics to make it seem like the the image they've created is coming from infinity.

The second issue is that you can't just turn infra-red photons into visible photons without a source of energy, which in this technique is provided by a strong near-infrared pump beam from a high-power laser diode. Just because you can't see that doesn't mean it's a good idea to shine it anywhere near your eyes.

Alternatively you could use a strong visible-light beam and just shine it directly at whatever the f.ck you want to see.

Of course their work is useful and has applications but the night-vision goggles thing is just a pathetic bid for attention from a press release.
It seems to me that the claims of "regular glasses [turned into] night vision goggles" are coming from the newspaper, rather than the researchers, who just seem to claim that they'd be able to make night vison goggles lighter/more compact, which seems a fair enough possibility, even if more work is needed.

It seems that this works in a similar way to photocathode bswed IR viewers which focuses an image onto a photocathode, which then emits (typically green) light which then goes through more optics, so your eye can focus the image on the retina. This experiment describes a similar process, but the photocathode is replaced with this InGAs film that converts the frequency of the incident photons. But if they could get it to work without having to focus the beam then you could do away with much of the optics. But for that to work, it'd have to work at low light levels, and retain the phase information. This experiment was done with very high light levels (especially if you look at peak power, rather than average, cos they were using a pulsed source).

With these sort of nonlinear things for frequency conversion, the output photons have the same direction has the incident photons, so that's not a problem. If this was not the case, things like frequency doubling a laser beam and optical parametric oscillators wouldn't work in a useful way (or not a useful way for how they are used, I guess). Nether is the pump light getting to your eye, you could just stick a filter there to get rid of it - in fact, they do this in their setup (see supplementary material).

This actually seems pretty cool to me. It has more potential uses than just night vision goggles. I'm thinking of one right now, which would be proper useful for me.

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Re: Night-vision goggles

Post by shpalman » Tue Jun 15, 2021 8:24 pm

Boustrophedon wrote:
Tue Jun 15, 2021 8:19 pm
Nothing to do with the above paper, which I don't understand anyway: I don't understand why IR vision equipment is so expensive, given that most of the camera chips in use are quite sensitive in the near IR anyway, and have to be equipped with IR filters to correct for this.
Night vision needs longer wavelengths (thermal imaging needs much longer wavelengths). To exploit inexpensive NIR sensitivity you tend to need those big IR floodlights.
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Re: Night-vision goggles

Post by monkey » Tue Jun 15, 2021 8:28 pm

Also, I wish photographers would stop taking pictures of people who do optics by getting them to put the googles on and pretend to be adjusting stuff.

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Re: Night-vision goggles

Post by monkey » Tue Jun 15, 2021 8:33 pm

shpalman wrote:
Tue Jun 15, 2021 8:24 pm
Boustrophedon wrote:
Tue Jun 15, 2021 8:19 pm
Nothing to do with the above paper, which I don't understand anyway: I don't understand why IR vision equipment is so expensive, given that most of the camera chips in use are quite sensitive in the near IR anyway, and have to be equipped with IR filters to correct for this.
Night vision needs longer wavelengths (thermal imaging needs much longer wavelengths). To exploit inexpensive NIR sensitivity you tend to need those big IR floodlights.
You get pretty much nothing with Silicon detectors past 1 um, even if your source is stupid bright. InGAs is good from 1 - 1.7 um, IRC, but is more expensive and noisy. It also wears out just by sitting on the shelf.

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Re: Night-vision goggles

Post by shpalman » Tue Jun 15, 2021 9:06 pm

monkey wrote:
Tue Jun 15, 2021 8:22 pm
shpalman wrote:
Tue Jun 15, 2021 6:45 pm
Ultra-thin film won't actually turn regular glasses into night vision goggles for a couple of good reasons I'm about to give you

The (open-access) article is at https://doi.org/10.1117/1.AP.3.3.036002

The first issue is that unless you can turn the infra-red photons into visible photons going in exactly the same direction, all you'll do is make the film on your glasses glow diffusely. Part of the reason why night-vision goggles are bulky and heavy is that they need the optics to make it seem like the the image they've created is coming from infinity.

The second issue is that you can't just turn infra-red photons into visible photons without a source of energy, which in this technique is provided by a strong near-infrared pump beam from a high-power laser diode. Just because you can't see that doesn't mean it's a good idea to shine it anywhere near your eyes.

Alternatively you could use a strong visible-light beam and just shine it directly at whatever the f.ck you want to see.

Of course their work is useful and has applications but the night-vision goggles thing is just a pathetic bid for attention from a press release.
It seems to me that the claims of "regular glasses [turned into] night vision goggles" are coming from the newspaper...
https://www.eurekalert.org/pub_releases ... 061521.php
monkey wrote:
Tue Jun 15, 2021 8:22 pm
... rather than the researchers, who just seem to claim that they'd be able to make night vison goggles lighter/more compact, which seems a fair enough possibility, even if more work is needed.
If a person were to wear glasses fitted with the film during the day, they would still be able to see what is normally visible to the naked eye, she said. “On top of that, you would see some infrared information.”
monkey wrote:
Tue Jun 15, 2021 8:22 pm
It seems that this works in a similar way to photocathode bswed IR viewers which focuses an image onto a photocathode, which then emits (typically green) light which then goes through more optics, so your eye can focus the image on the retina. This experiment describes a similar process, but the photocathode is replaced with this InGAs film that converts the frequency of the incident photons. But if they could get it to work without having to focus the beam then you could do away with much of the optics. But for that to work, it'd have to work at low light levels, and retain the phase information. This experiment was done with very high light levels (especially if you look at peak power, rather than average, cos they were using a pulsed source).

With these sort of nonlinear things for frequency conversion, the output photons have the same direction has the incident photons, so that's not a problem. If this was not the case, things like frequency doubling a laser beam and optical parametric oscillators wouldn't work in a useful way (or not a useful way for how they are used, I guess). Nether is the pump light getting to your eye, you could just stick a filter there to get rid of it - in fact, they do this in their setup (see supplementary material).
Their pump beam is parallel to the signal beam although I think they do mention that it could be anti-parallel. Of course they need to filter it before it hits the detector.

Fair enough that it conserves momentum. Will these sub-micron structures in a high refractive index material cause wide diffraction of the beam though?
monkey wrote:
Tue Jun 15, 2021 8:22 pm
This actually seems pretty cool to me. It has more potential uses than just night vision goggles. I'm thinking of one right now, which would be proper useful for me.
Well, it's interesting. I'm not sure why nothing quite like this has come out of our department given how much they're interesting in plasmonics and how much we're interested in infra-red applications of semiconductors.
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Re: Night-vision goggles

Post by monkey » Tue Jun 15, 2021 10:15 pm

I'm getting confused with quotes, so I'm not bothering.

On the bit about glasses:

Fair do's. I honestly don't remember that quote, but I must've read it because I do remember wondering why they bothered with the "Gallium arsenide is a common semiconductor and has been used for decades in transistors and solar cells." bit that came just after. They do seem to be stretching things past breaking point. That Eureka alert article is worse than the Guardian one just because of the picture, which was made by one of the authors.

I have noticed a tendency for some researchers to aim for something basically impossible - like night vision glasses (not goggles) - knowing that they'd never get there, but hoping that they come up with some useful stuff trying. Think it might be the influence of silicon valley types (one guy I know who thinks like this is an ex-Silicon valley type). That might be going on here.

On the diffraction:

I don't think you'll get the sharpest image from this, and they did do some modelling of the diffraction in the paper, see the supplement. But you might be ok sacrificing image quality, if something else is important to you, like sensitivity.

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Re: Night-vision goggles

Post by Bird on a Fire » Tue Jun 15, 2021 11:00 pm

In terms of "night vision" goggles, at an old work project we've been having a lot of success with thermal telescopes. As in, you can identify a 15cm long, 100g bird from 100m away, because light and dark feathers have a different thermal signature so you get enough detail to ID similar species. If you wanted to see what a person was up to, or where their car goes, or when their door opens, from a few hundred meters away, thermal vision will let you do that with no need for IR.

(I'm sure Don's not up to anything weird.) In terms of birds, one quite interesting result has been finding large flocks of shy waders like curlews feeding right in front of busy waterfronts at night, when they'd never hand out there in the day because of disturbance. At night they don't mind you walking much closer. It means our maps of what habitat waterbirds use may be hugely underestimating the importance of more urbanised/disturbed areas (during winter they can be getting over half their energy from nocturnal foraging).

I don't know any of the physics, though. Presumably there are limits to how far a thermal signature can carry compared to a visible-light/IR one, but I can't imagine spotlighting an estuary with IR floods at night would be easier or cheap by comparison.
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Re: Night-vision goggles

Post by dyqik » Tue Jun 15, 2021 11:16 pm

Bird on a Fire wrote:
Tue Jun 15, 2021 11:00 pm
(I'm sure Don's not up to anything weird.)
I'd be very disappointed if he isn't.

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Re: Night-vision goggles

Post by Bird on a Fire » Tue Jun 15, 2021 11:51 pm

Bare in mind I'm baselining "weird" with birdwatching.
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Re: Night-vision goggles

Post by WFJ » Wed Jun 16, 2021 6:37 am

monkey wrote:
Tue Jun 15, 2021 8:28 pm
Also, I wish photographers would stop taking pictures of people who do optics by getting them to put the googles on and pretend to be adjusting stuff.
Next you'll be telling me that chemists don't spend their working day holding conical flasks of brightly coloured solutions up to their eyes to inspect them closely.

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Re: Night-vision goggles

Post by dyqik » Thu Jun 17, 2021 10:53 am

WFJ wrote:
Wed Jun 16, 2021 6:37 am
monkey wrote:
Tue Jun 15, 2021 8:28 pm
Also, I wish photographers would stop taking pictures of people who do optics by getting them to put the googles on and pretend to be adjusting stuff.
Next you'll be telling me that chemists don't spend their working day holding conical flasks of brightly coloured solutions up to their eyes to inspect them closely.
I've spent some time this week looking through a telescope. At the inside of a cryostat.

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Re: Night-vision goggles

Post by monkey » Thu Jun 17, 2021 12:55 pm

WFJ wrote:
Wed Jun 16, 2021 6:37 am
monkey wrote:
Tue Jun 15, 2021 8:28 pm
Also, I wish photographers would stop taking pictures of people who do optics by getting them to put the googles on and pretend to be adjusting stuff.
Next you'll be telling me that chemists don't spend their working day holding conical flasks of brightly coloured solutions up to their eyes to inspect them closely.
I do actually spend a lot of time with googles on and adjusting mirrors. But it's still a cliché.

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