Night-vision device
A night-vision device (NVD), also known as night optical/observation device (NOD) and night-vision goggles (NVG), is an optoelectronic device that allows images to be produced in levels of light approaching total darkness. The image may be a conversion to visible light of both visible light and near-infrared, while by convention detection of thermal infrared is denoted thermal imaging. The image produced is typically monochrome green, because it was considered to be the easiest color to look at for prolonged periods in the dark. NVDs are most often used by the military and law  enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system. Many NVDs include a protective sacrificial lens, or optical components such as telescopic lenses or mirrors. An NVD may have an IR illuminator, making it an active as opposed to passive night-vision device. They are often used in conjunction with IR laser sights which project a beam onto the target that is only visible through an NVD. Night-vision devices were first used in World  War II and came into wide use during the Vietnam War. The technology has evolved greatly since their introduction, leading to several "generations" of night-vision equipment with performance increases and price reductions. Consequently, they are available for a wide range of applications, e.g. for gunners, drivers and aviators. History. US manufacturers, through the US government, have introduced a retrospective classification of NVDs into "generations". Under this periodization, the period prior to the end of World War II has sometimes been described as Generation 0. In 1929 Hungarian physicist Kálmán Tihanyi invented an infrared-sensitive electronic television camera for anti -aircraft defense in the UK. Night-vision devices were introduced in the German Army as early as 1939 and were used in World War II. AEG started developing the first devices in 1935. In mid-1943, the German Army began the first tests with infrared night-vision () devices and telescopic rangefinders mounted on Panther tanks. Two different arrangements were constructed and used on Panther tanks. The Sperber FG 1250 ("Sparrow Hawk"), with a range of up to 600 m, had a 30 cm infrared searchlight and an image converter operated by the tank commander. An experimental Soviet device called the PAU-2  was field-tested in 1942. From late 1944 to March 1945 the German military conducted successful tests of FG 1250 sets mounted on Panther Ausf. G tanks (and other variants). Before World War II ended in 1945, approximately 50 (or 63) Panthers had been equipped with the FG 1250 and saw combat on both the Eastern and Western Fronts. The "Vampir" man-portable system for infantry was used with StG 44 assault rifles. Parallel development of night-vision systems occurred in the US. The M1 and M3 infrared night-sighting devices, also known as the "sniperscope" or "snooperscope", saw limited  service with the US Army in World War II and in the Korean War, to assist snipers. These were active devices, using a large infrared light source to illuminate targets. Their image-intensifier tubes used an anode and an S-1 photocathode, made primarily of silver, cesium, and oxygen, and electrostatic inversion with electron acceleration was used to achieve gain. Examples After World War II Vladimir K. Zworykin developed the first practical commercial night-vision device at Radio Corporation of America, intended for civilian use. Zworykin's idea came from a former radio-guided missile. At that time infrared was commonly  called "black light", a term later restricted to ultraviolet. Zworykin's invention was not a success due to its size and cost. United States. Generation 1. First-generation passive devices developed in the 1960s, introduced during the Vietnam War and patented by the US Army, were an adaptation of earlier active GEN 0 technology and relied on ambient light instead of using an extra infrared light source. Using an S-20 photocathode, their image intensifiers produced a light amplification of around 1000, but they were quite bulky and required moonlight to function properly. Examples: Generation 2 (GEN II). Second-generation devices  developed in the 1970s, featuring an improved image-intensifier tube using micro-channel plate (MCP) with an S-25 photocathode, and resulting in a much brighter image, especially around the edges of the lens. This led to increased illumination in low ambient-light environments, such as moonless nights. Light amplification was around . Also improved were image resolution and reliability. Examples: Later advances in GEN II technology brought the tactical characteristics of "GEN II+" devices (equipped with better optics, SUPERGEN tubes, improved resolution and better signal-to-noise ratios) into the range of GEN III devices, which has complicated comparisons. Generation 3  (GEN III). Third-generation night-vision systems, developed in the late 1980s, maintained the MCP from Gen II, but used a photocathode made with gallium arsenide, which further improved image resolution. In addition, the MCP is coated with an ion barrier film for increased tube life. However, the ion barrier causes fewer electrons to pass through, diminishing the improvement expected from the gallium-arsenide photocathode. Because of the ion barrier, the "halo" effect around bright spots or light sources is larger too. The light amplification is also improved to around –. Power consumption is higher than in GEN II tubes. Examples : Auto-gating. The ATG function was designed to improve the Bright-Source Protection (BSP) feature, to be faster, and to keep the best resolution and contrast at all times. It is particularly suitable for aviator's night-vision goggles, for operations in urban areas or for special operations. ATG is a unique feature that operates constantly, electronically reducing the "duty cycle" of the photocathode voltage by very rapidly switching the voltage on and off. This maintains the optimal performance of the I² tube, continuously revealing mission-critical details, safeguarding the I² tube from additional damage and protecting the user from  temporary blindness. The benefits of ATG can easily be seen not only during day–night–day transitions, but also under dynamic lighting conditions when rapidly changing from low-light to high-light conditions (above ), such as sudden illumination of dark room. A typical advantage of ATG is best felt when using a weapon sight, which experiences a flame burst during shooting (see figures below showing pictures taken at the impact zone of a dropped bomb). ATG would reduce the temporary blindness that a standard BSP tube would introduce, allowing personnel to continuously maintain "eyes on target". ATG provides added safety  for pilots when flying at low altitudes, and especially during takeoffs and landings. Pilots operating with night-vision goggles are constantly subjected to dynamic light conditions when artificial light sources, such as from cities, interfere with their navigation by producing large halos that obstruct their field of view. Generation 3+ (GEN III OMNI IV–VII). The US Army Night Vision and Electronic Sensors Directorate (NVESD) is part of the governing body that dictates the names of the generations of night-vision technologies. The NVESD was originally the Army Night Vision Laboratory (NVL), which worked within the US Army Research  Labs. Although the recent increased performance associated with the GEN-III OMNI-VI/VII components is impressive, the US Army has not yet authorized the use of the name GEN-IV for these components. GEN-III OMNI-V–VII devices developed in the 2000s can differ from standard generation 3 in one or both of two important ways: While the consumer market classifies this type of system as "generation 4", the United States military describes these systems as "generation 3 autogated" tubes (GEN-III OMNI-VII). Moreover, as autogating power supplies can now be added to any previous generation of  night-vision devices, "autogating" capability does not automatically class the devices as a GEN-III OMNI-VII. Any postnominals appearing after a generation type (i.e., Gen II+, Gen III+) do not change the generation type of the device, but instead indicate improvement(s) over the original specification's requirements. Examples: Figure of merit. In the late 1990s, innovations in photocathode technology significantly increased the signal-to-noise ratio, with newly developed tubes starting to surpass the performance of Gen 3 tubes. By 2001 the United States federal government concluded that a tube's "generation" was not a determinant factor of a  tube's global performance, making the term "generation" irrelevant in determining the performance of an image-intensifier tube, and therefore eliminated the term as a basis of export regulations. Though image-intensification technology employed by different manufacturers varies, from the tactical point of view, a night-vision system is an optical device that enables vision in conditions of low light. The US government itself has recognized the fact that technology itself makes little difference, as long as an operator can see clearly at night. Consequently, the United States bases export regulations not on the generations, but on a calculated factor  called "figure of merit" (FOM). A National Defense University document, "The NATO Response Force" (authored by Jeffrey P. Bialos, the Executive Director of the Transatlantic Security and Industry Program at the Johns Hopkins University, and Stuart L. Koehl, a Fellow at the Center for Transatlantic Relations of the same university) briefly describes the method of FOM calculation and its implications for export. US-made tubes with a FOM greater than 1400 are not exportable outside the US; however, the Defense Technology Security Administration (DTSA) can waive that policy on a case-by-case basis. Other technologies. The United States Air  Force experimented with panoramic night-vision goggles (PNVGs), which double the user's field of view to around 95° by using four 16 mm image-intensifier tubes, rather than the more standard two 18 mm tubes. They are in service with A-10 Thunderbolt II, MC-130 Combat Talon and AC-130U Spooky aircrew, and later evolved into Ground Panoramic Night Vision Goggles (GPNVG-18) that are also popular with special forces. The AN/PSQ-20, manufactured by ITT (also known as the Enhanced Night Vision Goggle, ENVG), seeks to combine thermal imaging with image intensification, as does the Northrop Grumman Fused Multispectral Weapon  Sight. A new technology is being introduced to the consumer market. First shown at the 2012 SHOT Show in Las Vegas, NV by Armasight. this technology, called Ceramic Optical Ruggedized Engine (CORE), produces a higher-performance Gen 1 tubes. The main difference between CORE tubes and standard Gen 1 tubes is introduction of a ceramic plate instead of a glass one. This plate is produced from specially formulated ceramic and metal alloys. Edge distortion is improved, photo sensitivity is increased, and the resolution can get as high as 60 /mm. CORE is still considered Gen 1, as it does not  utilize a microchannel plate. Scientists at the University of Michigan have developed a contact lens that can act as a night-vision device. The lens has a thin strip of graphene between layers of glass that reacts to photons to make dark images look brighter. Current prototypes only absorb 2.3% of light, so the percentage of light pickup has to rise before the lens can be viable. The graphene technology can be expanded into other uses, like car windshields, to improve night-driving. The US. Army is interested in the technology to potentially replace night-vision goggles. The Sensor and  Electron Devices Directorate (SEDD) of the US Army Research Laboratory developed quantum-well infrared detector (QWID) technology. This technology's epitaxial layers, which result in diode formation, compose a gallium arsenide or aluminum gallium arsenide system (GaAs or AlGaAs). It is particularly sensitive to infrared waves that are mid-long lengths. The Corrugated QWIP (CQWIP) broadens detection capacity by using a resonance superstructure to orient more of the electric field parallel, so that it can be absorbed. Although cryogenic cooling between 77 K and 85 K is required, QWID technology is considered for constant surveillance viewing due to its claimed  low cost and uniformity in materials. Materials from the II–VI compounds, such as HgCdTe, are used for high-performing infrared light-sensing cameras. In 2017 the US Army Research Labs in collaboration with Stony Brook University developed an alternative within the . InAsSb, a III–V compound, is commonly used commercially for opto-electronics in items such as DVDs and cell phones. To counteract this possibility in implementing InAsSb, scientists added a graded layer with increased atomic spacing and an intermediate layer of the substrate GaAs to trap any potential defects. This technology was designed with night-time military operations  in mind. The Enhanced Night Vision Goggle-Binoculars (ENVG-B), manufactured by L3Harris Technologies, provide an improved capability to observe in all weather-conditions, in addition to higher resolution, as white phosphor tubes offer a better contrast compared to the traditional green phosphor ones. Soviet Union and Russia. The Soviet Union, and after 1991 the Russian Federation, have developed a range of night-vision devices. Models used after 1960 by the Russian/Soviet Army are designated "1PNxx" (xx), where "1PN" is the GRAU index of night-vision devices. The PN stands for "pritsel nochnoy" (), meaning "night sight", and the "xx