Image Intensifier
An image intensifier (abbreviation: II or I²) is an electro-optical component that can produce an intensified monochrome image on a phosphor screen from a cone of incoming light, intended to intensify the signal beyond what optics and digital sensors are capable of.
In the field of night vision, image intensifier refers to image intensifier tubes which are miniaturized image intensifiers (usually in tubular shape) that form the core component of any night vision device.
Image intensifier tubes are inserted into a housing that otherwise only provides optics, power supply, and protection of the sensitive component. Many formats of image intensifier tubes are designed to be exchangable with limited tooling and know-how, originally intended to allow armies to replace damaged image intensifier tubes by an engineer during deployment.
Generations
The U.S. Army's Night Vision and Electronic Sensors Directorate (NVESD) categorizes image intensifiers into four distinct generations. With each generation, a change in the technology has lead to substantial performance improvements.[1]
Although the generation of any given image intensifier will quickly provide a rough understanding of what to expect from it, it is not a replacement for accurate performance parameters (e.g. FOM, SNR, Gain), as these can vary wildly for different image intensifiers of the same generation. The relevant agencies of the U.S. government have since recognized this circumstance and have mostly stopped using generations to refer to image intensifiers in their specifications, and instead use the Figure of Merit (FOM) for most purposes.
Some manufacturers and retailers use a + to indicate intra-generational improvements, e.g. Gen. 2+. This practice is not part of the official specification and can be defined differently by anyone.
Generation 0
Generation 0 was invented in 1929 by a hungarian scientist in the UK. First uses where in World War II by the Germans, later the Soviets and the Americans.
Gen. 0 tubes don't have any or only very low gain of a around 10 and thus rely on strong IR ilumination.
Examples of Gen 0 devices
- Vampir
- M2 & M3 Sniperscope
- PNV57A
Generation 1
Generation 1, developed and patented in the 1960s, improved the gain to around 1000. This enabled the use of Gen. 1 devices under moonlight conditions without the use of IR illumination.
Later developments include the glass in the body being replaced with ceramic, improving the gain even further. These devices are sometimes referred to as Gen. 1+.
Some devices used multiple tubes in a cascade configuration, leading to improvements in gain of up to 100,000.
Examples of Gen 1 devices
- AN/PAS 2 Starlight
- Armasight Spark
- PNV57H
Gen. 1 technology is also found in most cheap consumer devices.
Generation 2
The Generation 2 was developed in the 1970s and was the first generation using a Microchannel Plate (MCP), which substantially increased the gain to around 20k. During this time, due to drastic innovations in the semiconductor space, the first widespread integration of the PSU with the tube in a single, modern package appears.
Generation 2 IITs are usually produced with either P22, P43 or P45 phosphor screens.
Examples of Gen 2 devices
- GN-1 employed Gen 2 IIT upon release.
Generation 3
The photocathode is made using gallium arsenide and the refined MCP technology is coated with an Aluminum oxide layer called ion barrier film to prolong the tubes functional life by preventing the occasionally released ion to damage the MCP, a process called ion-poisoning which drastically diminishes the plates functional lifespan. The downside of this ion film is that it somewhat restricts the amount of electrons that pass through it thereby detracting some of the intensification. The so called haloing-effect was also increased by this film, something that lessens the practical performance since it may obscure parts of what is being observed.
Subsequent development of the technology led to "thin-film" tubes among other solutions to lessen the impact of the ion barrier on gain and resolution. Since the beginnings of thin-film IIT it has become so commonplace that instead of being singled out as having thin ion barrier film the earlier image intensifiers are nowadays referred to as "thick-film" instead.
Gen. 3 tubes are usually produced with either P43 or P45 phosphor screens. Adams Industries sells devices with modified image intensifiers featuring a bichromatic (two-color) phosphor screen.[2]
Gain averages between 30k to 50k.
Examples of Gen 3 devices
Filmless
As a logical next step, manufacturer L3 (now L3Harris) began developing third generation image intensifiers without an ion barrier film before the year 2000. Albeit successful in creating even higher performing image intensifiers, the early iterations suffered from shorter lifespans and less durability in addition to higher production cost. To this day the U.S. military did not choose to award any larger procurement contracts for filmless image intensifiers, but instead exclusively for thin-film image intensifiers. Only the most recently developed Omnibus procurement contract(s) are believed to involve filmless technology to some degree, but this remains unconfirmed. However, it is certain that some units of the U.S. military, e.g. special forces, have been equipped with devices featuring filmless image intensifiers since the early 2000s. This explains why filmless image intensifiers are being actively developed, produced and sold (even to civilians in the U.S.) under the label Unfilmed by L3Harris.
L3Harris stands out as the sole western producer of filmless image intensifier tubes, having patented the process. The only other eastern producer is Ekran FEP.
Generation 4
The official specification does not include Generation 4, as even the most modern filmless image intensifier tubes still fall under the definition of Generation 3.
Formats
- Mx9916 (Fat Anvis)
- MX-10130
- MX-10160 / Small Anvis / 37mm / 18mm
- MX-11769
- SwaP (16mm)
References
- ↑ Night Vision Technologies Handbook https://www.dhs.gov/sites/default/files/publications/NV-Tech-HB_1013-508.pdf
- ↑ https://www.adamsindustries.com/
