Are there actually nightvision scopes with wavelengths above 14um?

[Ben321]

I can't find it now, but I swore I remembered seeing somewhere either on an article or Youtube video, that the military's thermal night vision scope's used as sights on their rifles aren't standard LWIR scopes (wavelengths between 8um and 14um), but rather used much longer wavelengths (I think it was something like 17um or 19um) and that these were being upgraded to something over 20um. Now that I'm looking again for this information though, despite all my Google searching, I can't find that video or article anywhere on the internet. Maybe somebody here would have some info on such technology, being that this is a forum section about thermal infrared imagers.

Would it even be possible to build such a thermal imager though, in such a small package as a handheld scope or rifle-mounted scope? I mean the longer the wavelength, the more it gets emitted (at room temperature that is), so if the wavelengths is too long you end up with just a bunch of noise in the image (requiring cryo cooling of the sensor to bring the noise level down, and cryo coolers are quite bulky). And I also have no idea what material would be sensitive to such a wavelength. VOX microbolometers are sensitive between about 8um and 14um., far too short of a wavelength for anything near 20um

Anybody else here have info on such super long wavelength IR imagers?

[Vipitis]

So Long range thermal vision? There is. A lot of military application. For missile systems. There is also weapon scopes and handheld binoculars or really small monoculars like the flir scout series.


I found a YouTube channel who apparently self built thermal optics and fits them on various thermal cameras, and even flir one phone add-ons.

https://youtu.be/pc7ZwEyY5rA

I believe he has a account in this forum as well.

I contacted him yesterday in a YouTube comment to find out more about his scopes as I was trying to build a telescope for my CAT S60

[Kleinstein]

With a normal temperature, the maximum in thermal radiation is somewhere around 10 µm. So it does not make much sense to use exclusively longer wavelengths. However on can widen the wavelength range somewhat to longer wavelengths. However lens materials are also limited.

For the sensors there are thermal ones, that are in principle sensitive to any wavelength and only the window and maybe absorber is liming the range. These could be made to work with longer wavelength too.
The other class of detects use semiconductors and thus are limited to wavelengths below a certain material specific wavelengths. Here the detectors for longer wavelength need more cooling an generally have less sensitivity for the shorter wavelengths. So materials for more than about 15 µm are not that attractive, as the overall sensitivity will go down unless cooled to very low temperature (which is not practical for a portable application).

[coppice]

9um to 14um is OK for seeing at night, but its a poor frequency range for seeing through smoke, and seeing through smoke is a bigger priority for the military than seeing at night.

The bigger the particulates forming the smoke the longer the wavelength you need to see through it, so the enemy tries to make their smoke screen particles as big as possible, and it becomes a cat and mouse game. Even the fire services, trying to see through natural smoke, want wavelengths longer than 14um.

[CatalinaWOW]

The following link shows typical atmospheric transmission.  It shows why no one on earth would be very interested in longer wavelengths.

http://www.coseti.org/atmosphe.htm

Combine that with much lower emissions at these wavelengths and you see why you had trouble finding anything.

Now if you are on some other planet with lower average temperatures and a different atmosphere you might be on to something.

[Bill W]

And all fire service cameras are 8-14 because it sees through smoke so well.

the only thing you see is hot lumpy bits flying around.

Bill