Night-vision device

thumb|A [[United States Navy|US Navy aviator uses a pair of helmet-mounted AN/AVS-6 vision goggles. The effect on the natural night vision of the eye is evident]]

thumb|A standard [[telescopic sight augmented with a night-vision device in front on the M110. Note that in addition to the image intensifier, the NVD gathers much more light by its much larger aperture]]

thumb|A [[1PN51-2 night-vision reticle with markings for range estimation]]

thumb|First-person view through night-vision goggles of the FBI Hostage Rescue Team using an airboat.

A night-vision device (NVD), also known as a night optical/observation device (NOD) or night-vision goggle (NVG), is an optoelectronic device that allows visualization of images in low levels of light, improving the user's night vision.

The device enhances ambient visible light and converts near-infrared light into visible light which can then be seen by humans; this is known as I2 (image intensification). By comparison, viewing of infrared thermal radiation is referred to as thermal imaging and operates in a different section of the infrared spectrum.

A night vision device usually consists of an image intensifier tube, a protective housing, and an optional mounting system. Many NVDs also include a protective sacrificial lens, mounted over the front/objective lens to prevent damage by environmental hazards, while some incorporate telescopic lenses. An NVD image is typically monochrome green, as green was considered to be the easiest color to see for prolonged periods in the dark. Night vision devices may be passive, relying solely on ambient light, or may be active, using an IR (infrared) illuminator.

Night vision devices may be handheld or attach to helmets. When used with firearms, an IR laser sight is often mounted to the weapon. The laser sight produces an infrared beam that is visible only through an NVD and aids with aiming. Some night vision devices are made to be mounted to firearms. These can be used in conjunction with weapon sights or standalone; some thermal weapon sights have been designed to provide similar capabilities.

These devices were first used for night combat in World War II and came into wide use during the Vietnam War. The technology has evolved since then, involving "generations" of night-vision equipment with performance increases and price reductions. Consequently, though they are commonly used by military and law enforcement agencies, night vision devices are available to civilian users for applications including aviation, driving, and demining.

History

In 1929 Hungarian physicist Kálmán Tihanyi invented an infrared-sensitive electronic television camera for anti-aircraft defense in the UK. Night vision technology prior to the end of World War II was later described as Generation 0.

Parallel development 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.

An experimental Soviet device called the PAU-2 was field-tested in 1942.

In 1938 the British Admiralty assumed responsibility for British military infra-red research. They worked with Philips until the fall of the Netherlands, then with Philips' UK subsidiary Radio Transmission Equipment Ltd., and finally with EMI, who in early 1941 provided compact, lightweight image converter tubes. By July 1942 the British had produced a binocular apparatus called 'Design E'. This was bulky, needing an external power pack generating 7,000 volts, but saw limited use with amphibious vehicles of 79th Armoured Division in the 1945 crossing of the Rhine. Between May and June 1943, 43rd (Wessex) Infantry Division trialled man-portable night vision sets, and the British later experimented with mounting the devices to Mark III and Mark II(S) Sten submachine guns. However, by January 1945 the British had only made seven infra-red receiver sets. Although some were sent to India and Australia for trials before the end of 1945, by the Korean War and Malayan Emergency the British were using night vision equipment supplied by the United States.

Early examples include:

FG 1250 Sperber
ZG 1229 Vampir
PAU-2
PNV-57A tanker goggles
SU-49/PAS-5

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 large size and high cost.

United States

Generation 1

thumb|An [[M16 rifle|M16A1 rifle fitted with the AN/PVS-2 Starlight scope]]

First-generation passive devices developed by the US Army in the 1960s were introduced during the Vietnam War. They were an adaptation of earlier active technology and relied on ambient light instead of using an extra infrared light source. Using an S-20 photocathode, their image intensifiers amplified light around -fold, but they were quite bulky and required moonlight to function properly.

Examples:

AN/PVS-1 Starlight scope
AN/PVS-2 Starlight scope

Generation 2

thumb|A cut-open and depotted AN/PVS-5, showing the components of a night-vision device. This device was manufactured in 2nd generation (5A to 5C) and 3rd generation (5D)

1970s second-generation devices featured an improved image-intensifier tube using a micro-channel plate (MCP) with an S-25 photocathode.

AN/PVS-5
SUPERGEN

Later advances brought GEN II+ devices (equipped with better optics, SUPERGEN tubes, improved resolution and better signal-to-noise ratios), though the label is not formally recognized by the NVESD.

AN/NVS-7
AN/PVS-10
AN/PVS-14
AN/PVS-17
CNVS-4949
PN-21K

Auto-gating

Autogating (ATG) rapidly switches the power supply's voltage to the photocathode on and off. These switches are rapid enough that they are not detectable to the human eye and peak voltage supplied to the night vision device is maintained.

A removed or greatly thinned ion barrier that decreases the number of electrons that are rejected by GEN III MCP, hence resulting in less image noise. The disadvantage to a thin or removed ion barrier is the overall decrease in tube life from a theoretical mean time to failure (MTTF) for standard Gen III type, to MTTF for thin film types. This loss is largely negated by the low number of image-intensifier tubes that reach of operation before requiring replacement.

The consumer market sometimes classifies such systems as Generation 4, and the United States military describes these systems as Generation 3 autogated tubes (GEN III OMNI V-IX). Moreover, as autogating power supplies can be added to any previous generation of night-vision devices, autogating capability does not automatically put the devices in a particular OMNI classification. Any postnominals appearing after a generation type (i.e., Gen II+, Gen III+) indicate improvement(s) over the original specification's requirements.

Examples:

AN/PVS-14
AN/PVS-22
NVS-22
Binocular Night Vision Device (BNVD) (AN/PVS-15, AN/PVS-21, AN/PVS-23, AN/PVS-31A/D)
Ground Panoramic Night Vision Goggle (GPNVG-18)

Figure of merit

Figure of merit (FoM) is a rough quantitative Figure of a NVD's effectiveness and clarity. It is calculated using the number of line pairs per millimeter that a user can detect multiplied by the image intensifier's signal-to-noise ratio (SNR).

In the late 1990s, innovations in photocathode, power supply and microchannel plate (MCP) technology significantly increased the SNR.

By 2001, the United States federal government concluded that a tube's generation was not a determinant performance factor, obsoleting the term as a basis of export regulations.

The US government has recognized the fact that the technology itself makes little difference, as long as an operator can see clearly at night.

International Traffic in Arms Regulations specify that among other limitations gen2 and higher generation tubes with a luminous sensitivity greater than 350 μA/lm are not exportable. However, the Defense Technology Security Administration (DTSA) can waive that policy on a case-by-case basis.

Fusion night vision

thumb|A comparison of I2 only night vision (above) and I2 plus thermal fusion (below)

Fusion night vision combines I2 (image intensification) with thermal imaging, which functions in the medium (MWIR 3–5 μm) and/or long (LWIR 8–14 μm) wavelength range. At the higher end, SiOnyx has produced digital color NVGs. The "Opsin" of 2022 has a form factor and helmet weight similar to an AN/PVS-14, but requires a separate battery pack. It offers a shorter battery life and lower sensitivity. It can however tolerate bright light and process a wider range of wavelengths.

Other technologies

Ceramic Optical Ruggedized Engine (CORE) produces higher-performance Gen 1 tubes by replacing the glass plate with a ceramic plate. This plate is produced from specially formulated ceramic and metal alloys. Edge distortion is improved, photo sensitivity is increased, and the resolution can be as high as 60 /mm. CORE is still designated Gen 1 as it does not use a microchannel plate.

A night-vision contact lens prototype places a thin strip of graphene between layers of glass that reacts to photons to brighten dark images. Prototypes absorb only 2.3% of light, which is considered not yet enough for practical use by its developers.

The Sensor and Electron Devices Directorate (SEDD) of the US Army Research Laboratory developed quantum-well infrared detector (QWID). This technology's epitaxial layers use a gallium arsenide (GaAs) or aluminum gallium arsenide system (AlGaAs) which are particularly sensitive to mid-length infrared waves. The Corrugated QWID (CQWID) 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 may be appropriate for continuous surveillance viewing due to its claimed low cost and uniformity in materials but it has yet to enter commercial production.

Materials from the II–VI compounds, such as HgCdTe, are used for high-performance infrared light-sensing cameras. An alternative within the III–V family of compounds is InAsSb, which is common in opto-electronics such as DVDs and mobile phones. A graded layer with increased atomic spacing and an intermediate layer of GaAs substrate can trap any potential defects.

Metasurface-based upconversion technology provides a night-vision film that weighs less than a gram and can be placed across ordinary glasses. Photons pass through a resonant non-local lithium niobate metasurface with a pump beam. The metasurface boosts the photons' energy, pushing them into the visible spectrum without converting them to electrons. Cooling is not required and visible and infrared light appear in a single image. Its frequency range is 1550-nm infrared to visible 550-nm light. Because, traditionally, night-vision systems capture side-by-side views from each spectrum, they can't produce identical images unlike films applied to ordinary glasses.

Soviet Union/Russia

thumb|Active night-vision scope NSP-2 mounted on an [[AKML]]

thumb|NSPU (1PN34) 3.5× night-vision scope mounted on an [[AK-74#Variants|AKS-74U]]

thumb|1PN93-2 night-vision scope mounted on a RPG-7D3

The Soviet Union, and after 1991 the Russian Federation, have developed their own 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 is the model number. Different models introduced around the same time use the same type of batteries and mounting mechanism. Multi-weapon models have replaceable elevation scales, with one scale for the ballistic arc of each. Supported weapons include the AK family, sniper rifles, light machine guns and hand-held grenade launchers.

1PN34 refractor-based night sight for a range of small arms and grenade launchers (photo)
1PN50 refractor-based night observation binoculars.
1PN51 reflector-based night sight for a range of small arms and grenade launchers.
1PN51-2 reflector-based night sight for the RPG-29.
1PN58 refractor-based night sight for a range of small arms and grenade launchers.
1PN93-2 reflector-based night sight for the RPG-7D3, see photo.
1PN110, a more recent (~Gen 3) night sight for the RPG-29.
1PN113, a night sight similar to the 1PN110, for the SV-98 sniper rifle.
1PN106 counter-sniper night sight for the SVD sniper rifle and its SVDS variant.
1PN119 counter-sniper night sight for the PKMN and Pecheneg light machine guns.
1PN120 counter-sniper night sight for the SVDK sniper rifle.
1PN121 counter-sniper night sight for the ASVK large caliber sniper rifle.
1PN123 counter-sniper night sight for the SV-98 sniper rifle.

Legal restrictions

Belgium: firearms legislation forbids night-vision devices that can be mounted on a firearm.
Czech Republic: not regulated. Previously only available for hunting.
Germany: law forbids such devices if their purpose is to be mounted on firearms except for hunting wild boars.
Iceland: night-vision devices for hunting is prohibited, although owning the devices is permitted.
India: civilian possession and trading of night-vision scopes is prohibited without permission from Union home ministry.
Netherlands: possession is not regulated, but night-vision devices mounted on firearms require a permit. Using mounted night-vision equipment for hunting requires a permit in the Veluwe for hunting wild boar.
New Zealand: rescue helicopter services use US-made Gen3 goggles for use only according to US export regulations. Use of NVD for shooting non-indigenous game animals, such as rabbits, hares, deer, pigs, tahr, chamois, goats, wallabies, is permitted.
United States: a 2010–2011 summary of state hunting regulations for the use of night-vision equipment in hunting listed 13 states in which the equipment is prohibited, 17 states with various restrictions (e.g. only for certain non-game species, and/or in a certain date range), and 20 states without restrictions. It did not summarize the regulations for thermal-imaging equipment.
California: possessing a device "designed for or adaptable to use on a firearm which, through the use of a projected infrared light source and electronic telescope, enables the operator thereof to visually determine and locate the presence of objects during the night-time" is a misdemeanor. This essentially covers scopes using Gen0 technology, but not subsequent generations.
Minnesota, as of 2014, "A person may not possess night vision or thermal imaging equipment while taking wild animals or while having in possession [an uncased and loaded weapon] that could be used to take wild animals." Law-enforcement and military use is exempt.

References

External links

TNVC guide to night vision generations and specifications on 19 July 2021
Nitewalker guide to night vision equipment on 15 August 2021
Night Vision Devices Modeling and Optimal Design on 6 May 2022