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[[Image:Ir_girl.png|thumb|right|350px|Image of two girls in mid-infrared ("thermal") light ([[false-color]])]]
'''Infrared''' ('''IR''') radiation is [[electromagnetic radiation]] of a [[wavelength]] longer than that of [[visible light]], but shorter than that of [[radio waves]]. The name means "below [[red]]" (from the [[Latin]] ''infra'', "below"), red being the [[color]] of visible [[light]] with the longest wavelength. Infrared radiation has wavelengths between about [[1 E-7 m|750]] [[Nanometre|nm]] and 1 [[millimetre|mm]], spanning three orders of magnitude.<ref>{{cite web | author = Dr. S. C. Liew | url = http://www.crisp.nus.edu.sg/~research/tutorial/em.htm | title = Electromagnetic Waves | publisher = Centre for Remote Imaging, Sensing and Processing | language = English | accessdate = 2006-10-27 }}</ref>
The uses of infrared include military, such as: target acquisition, surveillance, homing and tracking and non-military, such as thermal efficiency analysis, remote temperature sensing, short-ranged wireless communication, [[spectroscopy]], and weather forecasting. [[Infrared astronomy]] uses sensor-equipped [[telescopes]] to penetrate dusty regions of space, such as [[molecular cloud]]s; detect cool objects such as [[planet]]s, and to view highly [[Redshift|red-shifted]] objects from the early days of the [[universe]].<ref name="ir_astronomy">{{cite web | url = http://www.ipac.caltech.edu/Outreach/Edu/importance.html | title = IR Astronomy: Overview | publisher = NASA Infrared Astronomy and Processing Center | language = English | accessdate = 2006-10-30 }}</ref>
At the atomic level, infrared energy elicits [[vibration]]al modes in a [[molecule]] through a change in the [[dipole moment]], making it a useful frequency range for study of these energy states. [[Infrared spectroscopy]] examines absorption and transmission of [[photon]]s in the infrared energy range, based on their frequency and intensity.<ref>{{cite web | last = Reusch | first = William | year = 1999 | url = http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm | title = Infrared Spectroscopy | publisher = Michigan State University | accessdate = 2006-10-27 }}</ref>
==Different regions in the infrared==
{{Unreferenced|date=July 2006}}
Objects generally emit infrared radiation across a spectrum of wavelengths, but only a specific region of the spectrum is of interest because sensors are usually designed only to collect radiation within a specific bandwidth. As a result, the infrared band is often subdivided into smaller sections. There are no standard divisions, but a commonly used scheme is:{{Fact|date=April 2007}}
*Near-infrared ('''NIR''', IR-A ''[[DIN]]''): 0.75-1.4 [[micrometer|µm]] in wavelength, defined by the water absorption, and commonly used in [[fiber optic]] telecommunication because of low attenuation losses in the SiO<sub>2</sub> glass ([[silica]]) medium. Image intensifiers are sensitive to this area of the spectrum, about 1 micron, 1,000 nanometers or 10,000 Angstroms. Examples include night vision devices such as night vision goggles.
*Short-wavelength infrared ('''SWIR''', IR-B ''DIN''): 1.4-3 µm, water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications
*Mid-wavelength infrared ('''MWIR''', IR-C ''DIN'') also called intermediate infrared (IIR): 3-8 µm. In guided missile technology this is the 'heat seeking' region in which the homing heads of passive IR homing missiles are designed to work, homing on to the IR signature of the target aircraft, typically the jet engine exhaust plume.
*Long-wavelength infrared ('''LWIR''', IR-C ''DIN''): 8–15 µm. About 10 microns is the "thermal imaging" region, in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and requiring no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared ([[FLIR]]) systems use this area of the spectrum. Sometimes also called the "far infrared."
*Far infrared ('''FIR'''): 15-1,000 µm (see also [[far infrared laser]])
NIR and SWIR is sometimes called ''reflected infrared'' while MWIR and LWIR is sometimes referred to as ''thermal infrared''. Due to the nature of the blackbody radiation curves, typical 'hot' objects, such as exhaust pipes, often appear brighter in the MW compared to the same object viewed in the LW.
Astronomers typically divide the infrared spectrum as follows:<ref>{{cite web
| author=IPAC Staff
| url = http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
| title = Near, Mid and Far-Infrared
| publisher = NASA ipac
| accessdate = 2007-04-04
}}</ref>
*'''near''': (0.7-1) to 5 µm
*'''mid''': 5 to (25-40) µm
*'''long''': (25-40) to (200-350) µm
These divisions are not precise and can vary depending on the publication. The three regions are used for observation of different temperature ranges, and hence different environments in space.
A third scheme divides up the band based on the response of various detectors:<ref name="Miller">Miller, ''Principles of Infrared Technology'' (Van Nostrand Reinhold, 1992), and Miller and Friedman, ''Photonic Rules of Thumb'', 2004.</ref>
*Near infrared ('''NIR'''): from 0.7 to 1.0 [[micrometre|micrometers]] (from the approximate end of the response of the human eye to that of silicon)
*Short-wave infrared ('''SWIR'''): 1.0 to 3 micrometers (from the cut off of silicon to that of the MWIR atmospheric window. InGaAs covers to about 1.8 micrometers; the less sensitive lead salts cover this region
*Mid-wave infrared ('''MWIR'''): 3 to 5 micrometers (defined by the atmospheric window and covered by InSb and HgCdTe and partially PbSe)
*Long-wave infrared ('''LWIR'''): 8 to 12, or 7 to 14 micrometers: the atmospheric window (Covered by HgCdTe and [[microbolometer]]s)
*Very-long wave infrared ('''VLWIR'''): 12 to about 30 micrometers, covered by doped silicon
These divisions are justified by the different human response to this radiation: near infrared is the region closest in wavelength to the radiation detectable by the human eye, mid and far infrared are progressively further from the [[visible spectrum|visible regime]]. Other definitions follow different physical mechanisms (emission peaks, vs. bands, water absorption) and the newest follow technical reasons (The common [[silicon]] detectors are sensitive to about 1,050 nm, while [[indium gallium arsenide|InGaAs]]' sensitivity starts around 950 nm and ends between 1,700 and 2,600 nm, depending on the specific configuration). Unfortunately, international standards for these specifications are not currently available.
[[Image:Atmospheric transmittance infrared.gif|right|frame|Plot of atmospheric transmittance in part of the infrared region.]]
The boundary between visible and infrared light is not precisely defined. The human [[eye]] is markedly less sensitive to light above 700 nm wavelength, so shorter frequencies make insignificant contributions to scenes illuminated by common light sources. But particularly intense light (e.g., from [[laser]]s, or from bright daylight with the visible light removed by colored gels[http://amasci.com/amateur/irgoggl.html]) can be detected up to approximately 780 nm, and will be perceived as red light. The onset of infrared is defined (according to different standards) at various values typically between 700 nm and 800 nm.
===Telecommunication bands in the infrared===
In [[optical communications]], the part of the infrared spectrum that is used is divided into several bands based on availability of light sources, transmitting/absorbing materials (fibers) and detectors:<ref>{{cite web | last = Ramaswami | first = Rajiv | date = May, 2002 | url = http://ieeexplore.ieee.org/iel5/35/21724/01006983.pdf | title = Optical Fiber Communication: From Transmission to Networking | publisher = IEEE | language = English | accessdate = 2006-10-18 }}</ref>
{| class="wikitable" style="Margin-left: auto; margin-right: auto;"
|-
!Band
!Descriptor
!Wavelength range
|-
|O band
|Original
|1260–1360 nm
|-
|E band
|Extended
|1360–1460 nm
|-
|S band
|Short wavelength
|1460–1530 nm
|-
|C band
|Conventional
|1530–1565 nm
|-
|L band
|Long wavelength
|1565–1625 nm
|-
|U band
|Ultralong wavelength
|1625–1675 nm
|}
The C-band is the dominant band for long-distance [[telecommunication]] networks. The S and L bands are based on less well established technology, and are not as widely deployed.
===Heat===
{{main|Thermal radiation}}
Infrared radiation is popularly known as "heat"<!--Do not wikilink incorrect use of term to correct meaning.--> or sometimes "heat radiation," since many people attribute all radiant heating to infrared light. This is a widespread misconception, since light and electromagnetic waves of any frequency will heat surfaces that absorb them. Infrared light from the Sun only accounts for 50%{{Fact|date=February 2007}} of the heating of the Earth, the rest being caused by visible light that is absorbed then re-radiated at longer wavelengths. Visible light or [[ultraviolet]]-emitting [[laser]]s can char paper and incandescently hot objects emit visible radiation. It is true that objects at room [[temperature]] will [[spontaneous emission|emit]] [[Thermal radiation|radiation]] mostly concentrated in the 8-12 micron band, but this is not distinct from the emission of visible light by incandescent objects and ultraviolet by even hotter objects (see [[black body]] and [[Wien's displacement law]]).<ref>{{cite web | last = McCreary | first = Jeremy |date=October 30, 2004 | url = http://dpfwiw.com/ir.htm | title = Infrared (IR) basics for digital photographers-capturing the unseen (Sidebar: Black Body Radiation) | publisher = Digital Photography For What It's Worth | accessdate = 2006-11-07 }}</ref>
[[Heat]] is energy in transient form that flows due to temperature difference. Unlike heat transmitted by [[thermal conduction]] or [[thermal convection]], radiation can propagate through a [[vacuum]].
The concept of [[emissivity]] is important in understanding the infrared emissions of objects. This is a property of a surface which describes how its thermal emissions deviate from the ideal of a [[blackbody]]. To further explain, two objects at the same physical temperature will not 'appear' the same temperature in an infrared image if they have differing emissivities.
== Applications ==
{{Unreferenced|date=July 2006}}
===Night vision===
Infrared is used in [[night-vision]] equipment when there is insufficient [[visible light]] to see an object. The radiation is detected and turned into an image on a screen, hotter objects showing up in different shades than cooler objects, enabling the [[police]] and military to distinguish warm targets, such as [[human being]]s and [[automobile]]s. ''Also see [[Forward looking infrared]]''. IR radiation is a secondary effect of heat; it is not heat itself. Heat itself is a measure of the translational energy of an amount of matter. "Thermal" detectors do not actually detect heat directly but the difference in IR radiation from objects. The device itself that detects the radiation is known as a [[photocathode]]. Military gunnery ranges sometimes use special materials that reflect IR radiation to simulate enemy vehicles with running engines. The targets can be at the exact same temperature as the surrounding terrain, but they emit (reflect) much more IR radiation. Different materials emit more or less IR radiation as temperature increases or decreases, depending on the composition of the material. Infrared imagery is usually formed as a result of the integrated inband intensity of the radiation, based on temperate and emissivity.
Simple infrared sensors were used by British, American and German forces in the [[Second World War]] as night vision aids for [[sniper]]s.
[[Smoke]] is more transparent to infrared than to visible light, so [[firefighter]]s use infrared imaging equipment when working in smoke-filled areas.
===Thermography===
[[Image:Infrared_dog.jpg|thumb|right|300px|A thermographic image of a dog]]
Infrared [[thermography]] is a non-contact, non-destructive test method that utilizes a thermal imager to detect, display and record thermal patterns and temperatures across the surface of an object. Infrared thermography may be applied to any situation where knowledge of thermal profiles and temperatures will provide meaningful data about a system, object or process. Thermography is widely used in industry for predictive maintenance, condition assessment, quality assurance, and forensic investigations of electrical, mechanical and structural systems. Other applications include, but are not limited to: law enforcement, firefighting, search and rescue, and medical and veterinary sciences.
Aside from test equipment, training is the most important investment a company will make in an infrared inspection program. Advances in technology have provided infrared equipment that is user-friendly; however, infrared thermography is not a "simply point and shoot" technology. In addition to understanding the object or system being inspected, thermographers must also understand common error sources that can influence observed thermal data. Typically,infrared training courses should cover the topics of infrared theory, heat transfer concepts, equipment selection and operation, how to eliminate or overcome common error sources, and specific applications. Training courses from independent training companies are preferred since they are not biased toward a single brand or type of equipment.
===Other imaging===
[[Image:Blue infrared light.jpg|thumb|300px|right|Infrared light from the [[LED]] of a [[remote control]] as seen by a digital camera.]] In [[infrared photography]], [[infrared filter]]s are used to capture the near-infrared spectrum. [[Digital camera]]s often use infrared [[blocker]]s. Cheaper [[digital camera]]s and some [[camera phones]] which do not have appropriate filters can "see" near-infrared, appearing as a bright white colour (try pointing a TV remote at your digital camera). This is especially pronounced when taking pictures of subjects near IR-bright areas (such as near a lamp), where the resulting infrared interference can wash out the image. There is also a technique called '[[Terahertz radiation|T-ray]]' imaging, which is imaging using far infrared or [[terahertz]] radiation. Lack of bright sources makes terahertz photography technically more challenging than most other infrared imaging techniques. Recently T-ray imaging has been of considerable interest due to a number of new developments such as [[terahertz time-___domain spectroscopy]].
===Heating===
Infrared radiation can be used as a deliberate heating source. For example it is used in [[infrared sauna]]s to heat the occupants, and also to remove ice from the wings of [[aircraft]] (de-icing). It is also gaining popularity as a method of heating asphalt pavements in place during new construction or in repair of damaged asphalt. Infrared can be used in cooking and heating food as it predominantly heats the opaque, absorbent objects, rather than the air around them.
Infrared heating is also becoming more popular in industrial manufacturing processes, e.g. curing of coatings, forming of plastics, annealing, plastic welding, print drying.
In these applications, infrared heaters replace convection ovens and contact heating. Efficiency is achieved by matching the wavelength of the [[infrared heater]] to the absorption characteristics of the material.
===Communications===
IR data transmission is also employed in short-range communication among computer peripherals and [[personal digital assistant]]s. These devices usually conform to standards published by [[Infrared Data Association|IrDA]], the Infrared Data Association. Remote controls and IrDA devices use infrared [[light-emitting diode]]s (LEDs) to emit infrared radiation which is focused by a plastic [[Lens (optics)|lens]] into a narrow beam. The beam is [[modulation|modulated]], i.e. switched on and off, to encode the [[data]]. The receiver uses a [[silicon]] [[photodiode]] to convert the infrared radiation to an electric [[Current (electricity)|current]]. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms. Infrared is the most common way for [[remote control]]s to command appliances.
[[Free space optics|Free space optical]] communication using infrared [[laser]]s can be a relatively inexpensive way to install a communications link in an urban area operating at up to 4 gigabit/s, compared to the cost of burying fiber optic cable.
Infrared lasers are used to provide the light for [[optical fiber]] communications systems. Infrared light with a wavelength around 1,330 nm (least [[Dispersion (optics)|dispersion]]) or 1,550 nm (best transmission) are the best choices for standard [[silica]] fibers.
===Spectroscopy===
[[Infrared spectroscopy|Infrared vibrational spectroscopy]] (see also [[near infrared spectroscopy]]) is a technique which can be used to identify molecules by analysis of their constituent bonds. Each chemical bond in a molecule vibrates at a frequency which is characteristic of that bond. A group of atoms in a molecule (e.g. CH<sub>2</sub>) may have multiple modes of oscillation caused by the stretching and bending motions of the group as a whole. If an oscillation leads to a change in [[dipole]] in the molecule, then it will absorb a [[photon]] which has the same frequency. The vibrational frequencies of most molecules correspond to the frequencies of infrared light. Typically, the technique is used to study [[organic compound]]s using light radiation from 4000-400 cm<sup>-1</sup>, the mid-infrared. A spectrum of all the frequencies of absorption in a sample is recorded. This can be used to gain information about the sample composition in terms of chemical groups present and also its purity (for example a wet sample will show a broad O-H absorption around 3200cm<sup>-1</sup>).
===Meteorology===
[[Image:US IR satpic.JPG|thumb|left| IR Satellite picture taken 1315 Z on 15th October 2006. A [[weather front|frontal]] system can be seen in the [[Gulf of Mexico]] with embedded Cumulonimbus cloud. Shallower Cumulus and Stratocumulus can be seen off the [[Eastern Seaboard]].]]
[[Weather satellite]]s equipped with scanning radiometers produce thermal or infrared images which can then enable a trained analyst to determine cloud heights and types, to calculate land and surface water temperatures, and to locate ocean surface features. The scanning is typically in the range 10.3-12.5 µm (IR4 and IR5 channels).
High, cold ice cloud such as [[Cirrus]] or [[Cumulonimbus]] show up bright white, lower warmer cloud such as [[Stratus]] or [[Stratocumulus]] show up as grey with intermediate clouds shaded accordingly. Hot land surfaces will show up as dark grey or black. One disadvantage of infrared imagery is that low cloud such as stratus or [[fog]] can be a similar temperature to the surrounding land or sea surface does not show up. However using the difference in brightness of the IR4 channel (10.3-11.5 µm) and the near-infrared channel (1.58-1.64 µm), low cloud can be distinguished, producing a ''fog'' satellite picture. The main advantage of infrared is that images can be produced at night, allowing a continuous sequence of weather to be studied.
These infrared pictures can depict ocean eddies or vortices and map currents such as the Gulf Stream which are valuable to the shipping industry. Fishermen and farmers are interested in knowing land and water temperatures to protect their crops against frost or increase their catch from the sea. Even [[El Niño]] phenomena can be spotted. Using color-digitized techniques, the gray shaded thermal images can be converted to color for easier identification of desired information.
===Climatology===
In the field of climatology, atmospheric infrared radiation is monitored to detect trends in the energy exchange between the earth and the atmosphere. These trends provide information on long term changes in the earth's climate. It is one of the primary parameters studied in research into [[global warming]] together with [[solar radiation]].
A [[pyrgeometer]] is utilized in this field of research to perform continuous outdoor measurements. This is a broadband infrared radiometer with sensitivity for infrared radiation between approximately 4.5µm and 50µm.
[[Image:pyrgeometer_CGR4_instrument.gif|thumb|right|225px|Example of a pyrgeometer. Model shown CGR 4. Picture courtesy of Kipp & Zonen BV. www.kippzonen.com/pyrgeometer]]
===Astronomy===
[[Image:Spitzer- Telescopio.jpg|right|220px|thumb|The [[Spitzer Space Telescope]] is a dedicated infrared space observatory currently in orbit around the Sun. (Note the black side to the telescope, to maximize infrared radiation.) ''[[NASA]] image.'']]
{{main|infrared astronomy|far infrared astronomy}}
Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of [[optical astronomy]]. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid [[helium]].
The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected [[atmospheric window]]s. This limitation can be partially alleviated by placing the telescope observatory at a high altitude, or by carrying the telescope aloft with a balloon or an aircraft. Space telescopes do not suffer from this handicap, and so outer space is considered the ideal ___location for infrared astronomy.
The infrared portion of the spectrum has several useful benefits for astronomers. Cold, dark [[molecular cloud]]s of gas and dust in our galaxy will glow with radiated heat as they are irradiated by imbedded stars. Infrared can also be used to detect [[protostar]]s before they begin to emit visible light. Stars emit a smaller portion of their energy in the infrared spectrum, so nearby cool objects such as [[planet]]s can be more readily detected. (In the visible light spectrum, the glare from the star will drown out the reflected light from a planet.)
Infrared light is also useful for observing the cores of [[active galaxy|active galaxies]] which are often cloaked in gas and dust. Distant galaxies with a high [[redshift]] will have the peak portion of their spectrum shifted toward longer wavelengths, so they are more readily observed in the infrared.<ref name="ir_astronomy" />
===Art history and Archaeology===
[[Image:Jan van Eyck 001.jpg|thumb|right|200px|''[[The Arnolfini Portrait]]'' by [[Jan van Eyck]], [[National Gallery, London]]]]
Infra-red (as art historians call them) reflectograms are taken of paintings to reveal underlying layers, in particular the [[underdrawing]] or outline drawn to by the artist as a guide. This often uses [[carbon black]] which shows up well in reflectograms, so long as it has not also been used in the ground underlying the whole painting. Art historians are looking to see if the visible layers of paint differ from the under-drawing or layers in between - such alterations are called [[pentimento|pentimenti]] when made by the original artist. This is very useful information in deciding whether a painting is the prime version by the original artist or a copy, and whether it has been altered by over-enthusiatic restoration work. Generally the more pentimenti, the more likely a painting is to be the prime version. It also gives useful insights into working practices. [http://www.clevelandart.org/exhibcef/ConsExhib/html/grien.html]
Among many other changes in the [[Arnolfini Portrait]] of 1434 (right), his face was higher by about the height of his eye, hers was higher, and her eyes looked more to the front. Each of his feet was underdrawn in one position, painted in another, and then overpainted in a third. These alterations are seen in infra-red reflectograms.<ref>National Gallery Catalogues: The Fifteenth Century Netherlandish Paintings by Lorne Campbell, 1998, ISBN 185709171</ref>
Similar uses of infrared are made by archaeologists on various types of objects, especially very old written documents such as the [[Dead Sea Scrolls]], the Roman works in the [[Villa of the Papyri]], and the Silk Road texts found in the [[Mogao Caves|Dunhuang Caves]].<ref>[http://idp.bl.uk/pages/technical_resources.a4d International Dunhuang Project An Introduction to digital infrared photography and its application within IDP -paper pdf 6.4MB]</ref> Carbon black used in ink can show up extremely well.
===Biological systems===
[[Image:wiki_snake_eats_mouse.jpg|thumb|right|Thermographic image of a snake eating a mouse]]
The [[Crotalinae|pit viper]] is known to have two infrared sensory pits on its head. There is controversy over the exact thermal sensitivity of this biological infrared detection system.<ref> {{cite journal | title = Thermal Modeling of Snake Infrared Reception: Evidence for Limited Detection Range | author = B. S. Jones; W. F. Lynn; M. O. Stone | journal = Journal of Theoretical Biology | volume = 209 | issue = 2 | pages = 201-211 | year = 2001 | id = {{doi|10.1006/jtbi.2000.2256}}}}</ref><ref>{{cite journal | title = Biological Thermal Detection: Micromechanical and Microthermal Properties of Biological Infrared Receptors | author = V. Gorbunov; N. Fuchigami; M. Stone; M. Grace; V. V. Tsukruk | journal = Biomacromolecules | volume = 3 | issue = 1 | pages = 106-115 | year = 2002 | id = {{doi|10.1021/bm015591f}}}}</ref>
Other organisms that actively employ thermo-receptors are [[rattlesnake]]s (Crotalinae subfamily) and [[boa]]s (Boidae family), the [[Common Vampire Bat]] (''Desmodus rotundus''), a variety of [[jewel beetle]]s (''[[Melanophila acuminata]]'')<ref>{{cite journal | last =Evans | first =W.G. | title =Infrared receptors in ''Melanophila acuminata'' De Geer | journal =Nature | volume =202 | pages =211 | date =1966 | doi =10.1038/202211a0 | accessdate =2007-05-07}}</ref>, darkly pigmented butterflies (''[[Pachliopta aristolochiae]]'' and ''[[Troides rhadamathus plateni]]''), and possibly blood-sucking bugs (''[[Triatoma infestans]]'').<ref>{{cite journal | author=A.L. Campbell, A.L. Naik, L. Sowards, M.O. Stone | title=Biological infrared imaging and sensing | journal=Micron | year=2002 | volume=33 | issue=2 | pages=211-225 | url=http://dx.doi.org/10.1016/S0968-4328(01)00010-5 }}</ref>
==The Earth as an infrared emitter==
{{Unreferenced|date=July 2006}}
The [[Earth]]'s surface and the clouds [[absorption (electromagnetic radiation)|absorb]] visible and invisible radiation from the [[sun]] and re-emit much of the energy as infrared back to the [[Earth's atmosphere|atmosphere]]. Certain substances in the atmosphere, chiefly cloud droplets and [[water]] vapor, but also [[carbon dioxide]], [[methane]], [[nitrous oxide]], [[sulfur hexafluoride]], and [[chlorofluorocarbons]], absorb this infrared, and re-radiate it in all directions including back to Earth. Thus the [[greenhouse effect]] keeps the atmosphere and surface much warmer than if the infrared absorbers were absent from the atmosphere.
==History of infrared science==
{{Unreferenced|date=July 2006}}
{{cleanup-section|September 2006}}
The discovery of infrared radiation is ascribed to [[William Herschel]], the [[astronomer]], in the early [[19th century]]. Herschel published his results in 1800 before the UK Royal Society. Herschel used a [[Triangular prism (optics)|prism]] to [[refract]] light from the [[sun]] and detected the infrared, beyond the [[red]] part of the spectrum, through an increase in the temperature recorded on a [[thermometer]]. He was surprised at the result and called them "Calorific Rays". The term 'Infrared' did not appear until late in the 19th century.
Other important dates include:<ref name="Miller"/>
*1835: [[Macedonio Melloni]] makes the first thermopile IR detector;
*1859: [[Gustav Kirchhoff]] formulates the [[blackbody theorem]] <math>E=J(T,n)</math>;
*1873: [[Willoughby Smith]] discovers the photoconductivity of [[selenium]];
*1879: [[Stefan-Boltzmann law]] formulated empirically <math>\omega_T^4</math>
*1880s & 1890s: [[John Strutt, 3rd Baron Rayleigh|Lord Rayleigh]] and [[Wilhelm Wien]] both solve part of the blackbody equation, but both solutions are approximations that "blow up" out of their useful ranges. This problem was called the "UV Catastrophe and Infrared Catastrophe".
*1901: [[Max Planck]] published the [[blackbody equation]] and theorem. He solved the problem by quantizing the allowable energy transitions.
*Early 1900s: [[Albert Einstein]] develops the theory of the [[photoelectric effect]], determining the [[photon]]. Also [[William Coblentz]] in [[spectroscopy]] and [[radiometry]].
*1917: [[Case]] develops [[thallous sulfide]] detector; British develop the first [[infra-red search and track]] (IRST) in World War I and detect aircraft at a range of one mile;
*1935: Lead salts-early missile guidance in [[World War II]];
*1938: [[Teau Ta]]-predicted that the pyroelectric effect could be used to detect infrared radiation.
*1952: [[H. Welker]] discovers InSb;
*1950s: [[Paul Kruse (engineer)|Paul Kruse]] (at Honeywell) and Texas Instruments form infrared images before 1955;
*1950s and 1960s: Nomenclature and radiometric units defined by [[Fred Nicodemenus]], [[G.J. Zissis]] and [[R. Clark]], [[Jones]] defines ''D''*;
*1958: [[W.D. Lawson]] ([[Royal Radar Establishment]] in Malvern) discovers IR detection properties of HgCdTe;
*1958: [[Falcon (rocket)|Falcon]]<!-- a disambiguation page--> & [[AIM-9 Sidewinder|Sidewinder]] missiles developed using infrared and the first textbook on infrared sensors appears by Paul Kruse, et al.
*1962: [[J. Cooper]] demonstrated pyroelectric detection;
*1962: Kruse and [[? Rodat]] advance HgCdTe; Signal Element and Linear Arrays available;
*1965: First IR Handbook; first commercial imagers ([[Barnes, Agema]] {now part of [[FLIR Systems]] Inc.}; [[Richard Hudson (physicist)|Richard Hudson]]'s landmark text; F4 TRAM FLIR by [[Hughes Aircraft Company|Hughes]]; [[phenomenology]] pioneered by [[Fred Simmons]] and [[A.T. Stair]]; U.S. Army's night vision lab formed (now [[Night Vision and Electronic Sensors Directorate]] (NVESD), and [[Rachets]] develops detection, recognition and identification modeling there;
*1970: [[? Boyle]] & [[? Smith]] propose CCD at [[Bell Labs]] for [[picture phone]];
*1972: [[Common module program]] started by NVESD;
*1978: [[Pommernig]] & [[? Francis]] fabricate [[IRCCD]]s; [[US Common Module]] leads to a proliferation of IR Sensors in the U.S. military; commercial IR companies formed ([[Inframetrics]] in Boston, MA and [[FLIR Systems]] Inc. in Portland OR); Infrared imaging astronomy comes of age, observatories planned, IRTF on Mauna Kea opened; 32 by 32 and 64 by 64 arrays are produced in InSb, HgCdTe and other materials.
==See also==
{{wiktionary|infrared}}
<div class="references-small" style="-moz-column-count:2; column-count:2;">
*[[Night vision]]
*[[Infrared astronomy]]
*[[Infrared camera]]
*[[Infrared filter]]
*[[Infrared photography]]
*[[Infrared spectroscopy]]
*[[Infrared thermometer]]
*[[Thermography]]
*[[Terahertz radiation]]
*[[Thermographic camera]]
*[[Infrared homing]]
*[[Black body radiation]]
*[[Infrared signature]]
*[[pyrgeometer]]
</div>
==References==
<div class="references-small">
<references/>
</div>
==External links==
===Journals===
*[http://www.sciencedirect.com/science/journal/13504495 Infrared Physics and Technology] (Elsevier) (last access June 2005).
===Web sites===
*[http://www.flirthermography.com/industries/ List of infrared application examples broken down by industry from FLIR Systems]
*[http://scienceofspectroscopy.info/wiki/index.php?title=Infrared_Spectroscopy Infrared Spectroscopy] NASA ''Open Spectrum'' wiki site.
*[http://www.irda.org/ IrDA]Organization that creates low cost infrared data interconnection standards.
*[http://www.ocinside.de/html/modding/usb_ir_receiver/usb_ir_receiver.html How to build an USB infrared receiver to remote control PCs]
*[http://imagers.gsfc.nasa.gov/ems/infrared.html Infrared Waves]Detailed explanation of infrared light.
*[https://ewhdbks.mugu.navy.mil/ U.S. Navy - Electronic Warfare and Radar Systems Engineering Handbook] Source of transmittance diagram and further information on electro-optics.
{{EMSpectrum}}
[[Category:Electromagnetic spectrum]]
[[ar:أشعة تحت حمراء]]
[[bn:অবলোহিত বিকিরণ]]
[[bs:Infracrveno zračenje]]
[[bg:Инфрачервено излъчване]]
[[ca:Infraroig]]
[[cs:Tepelné záření]]
[[da:Infrarød stråling]]
[[de:Infrarotstrahlung]]
[[et:Infrapunakiirgus]]
[[es:Radiación infrarroja]]
[[eo:Infraruĝa radiado]]
[[eu:Infragorri]]
[[fa:فروسرخ]]
[[fr:Infrarouge]]
[[gl:Radiación infravermella]]
[[ko:적외선]]
[[hr:Infracrveno zračenje]]
[[io:Infrereda]]
[[id:Inframerah]]
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[[he:תת אדום]]
[[lv:Infrasarkanais starojums]]
[[ms:Inframerah]]
[[nl:Infrarood]]
[[ja:赤外線]]
[[no:Infrarød stråling]]
[[nn:Infraraud stråling]]
[[pl:Podczerwień]]
[[pt:Radiação infravermelha]]
[[ru:Инфракрасное излучение]]
[[sq:Rrezet infra të kuqe]]
[[simple:Infrared]]
[[sk:Infračervené žiarenie]]
[[sl:Infrardeče valovanje]]
[[sr:Инфрацрвена светлост]]
[[fi:Infrapunasäteily]]
[[sv:Infraröd strålning]]
[[ta:அகச்சிகப்பு கதிர்கள்]]
[[vi:Hồng ngoại]]
[[tr:Kızılötesi]]
[[uk:Інфрачервоне випромінювання]]
[[zh:红外线]]
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