F*cking magic, that's how. And the truth is after we break this down for you, and give you the best and most technical explanation that we can, those first two words are still going to feel the most accurate. "Image intensification", as it's formally called (because "night vision" can refer to several technologies, if you're a pedantic nerd), has been around in one for or another for almost 80 years now... since the late 1940's. We've made leaps and bounds in its effectiveness since then, but at it's core, it's still just basically an analog vacuum tube CRT television that's sensitive to infrared light.
In fact, of the technologies we can think of off the top of our head, night vision is probably the only one where analog still outranks digital. We explore the comparison a bit more in our blog "Analog vs Digital Night Vision", but for this article, let's just stick to traditional analog intensification tubes.
What is an Image Intensification (Night Vision) Tube?
Gen III has two basic format styles of tubes:
- MX11769: This is the most produced type of tube, and what you will find in 99% of military units, as well as all civilian monoculars, and most civilian binoculars. Military night vision devices like the PVS-14 or the PVS-31 both have adjustable gain, meaning you can adjust the output brightness of the night vision unit. Most people tend to just leave their gain on the highest setting, so this feature isn't present in some of the civilian night vision housings, like the RNVG.
- MX10160: A tube without a "pigtail", that allows for the adjustment of gain. This is either on, or it's off. This is also what the famous GPNVG-18 uses. The quad-tube device doesn't have manual gain functions, just a push-button on top to power the device on. It's also worth noting that 11769 tubes can be converted into 10160 tubes.
Gen III Night Vision Components
The foundation of any night vision device, the housing is exactly what it sounds like. It's going to host all the other components, a bit like a lower receiver of an AR-15. And these days there's more night vision housings on the market than ever before, with more being released every year. Night vision housings can span from a tried and true PVS-14 monocular, to the high speed DTNVS, or the rugged RNVG. Different housings serve different needs, and this is a topic all of its own.
Your optics are nearly as important as your image intensifier itself. After all, your tube can only amplify the light it receives, so if your optics have a small aperture or poor quality glass that blocks light, your night vision performance will suffer, no matter how good your tube is.
There's a wide range of optics, with the two most common types being PVS and ANVIS optics. Typically, PVS optics are for ground use, and ANVIS are utilized in aviation. Of course, this is just a general rule, and certain Special Missions Units have been known to use ANVIS units, especially early in the War on Terror. There's advantages and disadvantaged to each.
Your optics do two things. First, your objective lenses focus the incoming light onto the image intensifier, so that an accurate image is being portrayed. Secondly, your eyepiece lens will allow the image being output from your tube to be magnified and presented to you in a clear way. Usually there is an adjustable diopter as well, to adjust the view for each individuals eyes.
Alright, this is the main event. You probably knew a lot of the information up until this point (but we hope you've learned something). But the real magic in night vision comes from the intensifier tube. Without that, all you really have is a 1x magnification telescope strapped to your face, and telescopes have been around since 1608. Not exactly new technology.
A night vision image intensification tube is made up of a lot of different parts, but how night vision works comes down to three main parts. We've cut out sections on parts like the power supply, because if you're reading this article, you understand how a battery works in an electronic device. Nothing groundbreaking there. We also dropped a section on the fiber twist. It's just a piece of fiber optic glass that's been heated and twisted to make the image right-side up when you look at it. Exciting.
Oh sh*t, almost forgot. For the next sections, keep in mind that a human hair is about 100 microns thick....
This is the first thing that incoming light is going to encounter. This is a circular piece of glass about 5mm thick, with a Silicone Nitride coating on the front side to prevent light from reflecting, and getting as much of it as possible to pass to the rear of the glass...
...Where it will encounter a Gallium Arsenide (GaAs) crystal grown on the other side. No joke, the first step of your night vision is basically a high-tech rock candy. Gallium Arsenide is misted across the glass until it's about 5 microns thick. This acts as a bandpass filter, allowing wavelengths above 600nm to pass through (Infrared starts at 850nm).
On top of that crystalline layer, they put another Zinc infused GaAs layer, about 1-2 microns thick. This is the active layer, that will actually convert those light photons into electrons, which will be magnified later on. Finally, a layer of Cesium-Oxide (Cs2O) is laid over that's about one atom thick, which makes the photocathode more efficient with Negative Electron Affinity.
From here the electrons pass to the micro-channel plate. As complicated as the photocathode sounds, we're actually simplifying everything a fair bit.
The MCP actually isn't new technology, and it started with Gen 2 night vision. That said, they're a lot more advanced, lot more efficient, and a lot higher resolution than they used to be.
Compared to the phosphor plate, the micro-channel plate is pretty straightforward. It's exactly what it sounds like, a plate full of thousands of tiny channels that the electrons find themselves in, and electricity causes those electrons to multiply themselves. This is how the actual image intensification happens. And how is it made?
Ever seen a glassblower make a pipe? Think that, but on a microscopic level. An etch-able (dissolvable) glass is surrounded by a lead-silicate glass, and stretched into a long rod in a special glass-fiber furnace. They then put that fiber with more fibers, and stretch them all together again. They repeat this process until they are left with millions of fibers that they've arranged into hexagonal shapes (so the fiber bundles stack together easily).
From here they slice the bundle about 1/3rd of a millimeter thick, at an angle of six degrees, and then dissolve the etchable glass, which creates a small plate with millions of holes in it. That's how you get your micro-channels.
We're not done yet though. The plate gets a nichrome coating to making it conductive to electricity. Then, it's going to get the film that is exclusive to Gen 3 night vision. This film prevents damaging positively charged ions from continuing from the photocathode to the micro-channel plate, but the downside is it will block some of the electrons as well. This is why thin-filmed tubes perform better in very low light than standard or "thick-filmed" tubes, and also why L3s "Un-Filmed" (a bit of a misnomer, as it does still have a very thin layer of film), perform best under low light.
The ion-barrier film is created and floated on water, and then the water evaporates to leave the film on supports. The film is then placed on the input side of the MCP, and Aluminum Oxide is coated on to a thickness of 0.003 microns. The MCP is then sintered to create the aluminum oxide film.
Ok, we lied, that wasn't straightforward at all.
The final secret in the night vision sauce is the phosphor screen. And when we say this is more simple than the other two components, we actually mean it this time. A phosphor screen really isn't too much different than analog television, and the technology, including the production process, has been around for a long time now.
As the multiplied electrons exit the micro-channel plate, they strike the phosphor screen, which tuns them back into light photons that we can see. Except now, there's a whole lot more of them.
The tech is laughably simple for this part compared to the others. They essentially take a screen, put it at the bottom of a liquid solution, and allow the phosphor particles to settle and bind onto it. The phosphor coating ends up being about 8 microns thick, and then once the plate is dried, they use inert argon gas to apply a thin layer of aluminum, ensuring the screen has good conductivity.
Now, phosphor screens are made with several different formulas to exhibit different traits. Performance is measured by two criteria. Fluorescence is how bright the screen will glow when struck by electrons, and phosphorescence measures how long it will glow. The goal is to have a screen that puts out a fair amount of light, and allows the image to linger for just long enough to be recognized, but not long enough that it isn't rapidly replaced by new information. This period of time tends to be around 1 millisecond, which can be thought of in terms of a refresh rate. Phosphor screens are labeled with a "P" number, with three examples above.
This phosphor screen can be any color the manufacturer desires, with the two most common being Green vs White Phosphor. In fact, some manufacturers have even done dual color phosphor screens. This light from the phosphor screen is then focused by your eyepiece objective, and that's what you see. Many people think that you're seeing through night vision tubes, but what you're really looking at is a tiny glowing phosphor screen, and that's why you see in green or white.
How does Night Vision Autogating work?
Much like a surge protector plugged into your wall outlet. Autogating is always working in the background in conjunction with with your photocathode to maintain a constant output level. The millisecond it senses an output surge, it instantaneously cuts power down to a reasonable level. This is why movies that show night vision users being blinded by flashlights, or the lights in a building being tuned on, aren't accurate. Autogating would immediately cut down on the conversion from photons to electrons, and the image would look relatively the same to the user. This also prevents the device from damaging itself, but be warned, it's not a perfect precautionary measure. If you leave your night vision on in a bright light environment, it will permanently damage it. How quickly just depends on the brightness of the light source, and the duration and concentration of the exposure.
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