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Infrared

Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with waves that are just longer than those of red light (the longest waves in the visible spectrum), so IR is invisible to the human eye. IR is generally understood to include wavelengths from around 750 nm (400 THz) to 1 mm (300 GHz).[1][2] IR is commonly divided between longer-wavelength thermal IR, emitted from terrestrial sources, and shorter-wavelength IR or near-IR, part of the solar spectrum.[3] Longer IR wavelengths (30–100 μm) are sometimes included as part of the terahertz radiation band.[4] Almost all black-body radiation from objects near room temperature is in the IR band. As a form of electromagnetic radiation, IR carries energy and momentum, exerts radiation pressure, and has properties corresponding to both those of a wave and of a particle, the photon.

For other uses, see Infrared (disambiguation).

It was long known that fires emit invisible heat; in 1681 the pioneering experimenter Edme Mariotte showed that glass, though transparent to sunlight, obstructed radiant heat.[5][6] In 1800 the astronomer Sir William Herschel discovered that infrared radiation is a type of invisible radiation in the spectrum lower in energy than red light, by means of its effect on a thermometer.[7] Slightly more than half of the energy from the Sun was eventually found, through Herschel's studies, to arrive on Earth in the form of infrared. The balance between absorbed and emitted infrared radiation has an important effect on Earth's climate.


Infrared radiation is emitted or absorbed by molecules when changing rotational-vibrational movements. It excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared range.[8]


Infrared radiation is used in industrial, scientific, military, commercial, and medical applications. Night-vision devices using active near-infrared illumination allow people or animals to be observed without the observer being detected. Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space such as molecular clouds, to detect objects such as planets, and to view highly red-shifted objects from the early days of the universe.[9] Infrared thermal-imaging cameras are used to detect heat loss in insulated systems, to observe changing blood flow in the skin, to assist firefighting, and to detect the overheating of electrical components.[10] Military and civilian applications include target acquisition, surveillance, night vision, homing, and tracking. Humans at normal body temperature radiate chiefly at wavelengths around 10 μm. Non-military uses include thermal efficiency analysis, environmental monitoring, industrial facility inspections, detection of grow-ops, remote temperature sensing, short-range wireless communication, spectroscopy, and weather forecasting.

Nature[edit]

Sunlight, at an effective temperature of 5,780 K (5,510 °C, 9,940 °F), is composed of near-thermal-spectrum radiation that is slightly more than half infrared. At zenith, sunlight provides an irradiance of just over 1 kW per square meter at sea level. Of this energy, 527 W is infrared radiation, 445 W is visible light, and 32 W is ultraviolet radiation.[12] Nearly all the infrared radiation in sunlight is near infrared, shorter than 4 μm.


On the surface of Earth, at far lower temperatures than the surface of the Sun, some thermal radiation consists of infrared in the mid-infrared region, much longer than in sunlight. Black-body, or thermal, radiation is continuous: it radiates at all wavelengths. Of these natural thermal radiation processes, only lightning and natural fires are hot enough to produce much visible energy, and fires produce far more infrared than visible-light energy.[13]

Near-infrared: from 0.7 to 1.0 μm (from the approximate end of the response of the human eye to that of silicon).

Short-wave infrared: 1.0 to 3 μm (from the cut-off of silicon to that of the MWIR atmospheric window). covers to about 1.8 μm; the less sensitive lead salts cover this region. Cryogenically cooled MCT detectors can cover the region of 1.0–2.5 μm.

InGaAs

Mid-wave infrared: 3 to 5 μm (defined by the atmospheric window and covered by , InSb and mercury cadmium telluride, HgCdTe, and partially by lead selenide, PbSe).

indium antimonide

Long-wave infrared: 8 to 12, or 7 to 14 μm (this is the atmospheric window covered by HgCdTe and ).

microbolometers

Very-long wave infrared (VLWIR) (12 to about 30 μm, covered by doped silicon).

1830: made the first thermopile IR detector.[67]

Leopoldo Nobili

1840: produces the first thermal image, called a thermogram.[68]

John Herschel

1860: formulated the blackbody theorem .[69]

Gustav Kirchhoff

1873: discovered the photoconductivity of selenium.[70]

Willoughby Smith

1878: invents the first bolometer, a device which is able to measure small temperature fluctuations, and thus the power of far infrared sources.[71]

Samuel Pierpont Langley

1879: formulated empirically that the power radiated by a blackbody is proportional to T4.[72]

Stefan–Boltzmann law

1880s and 1890s: and Wilhelm Wien solved part of the blackbody equation, but both solutions diverged in parts of the electromagnetic spectrum. This problem was called the "ultraviolet catastrophe and infrared catastrophe".[73]

Lord Rayleigh

1892: Willem Henri Julius published infrared spectra of 20 organic compounds measured with a bolometer in units of angular displacement.

[74]

1901: published the blackbody equation and theorem. He solved the problem by quantizing the allowable energy transitions.[75]

Max Planck

1905: developed the theory of the photoelectric effect.[76]

Albert Einstein

1905–1908: published infrared spectra in units of wavelength (micrometers) for several chemical compounds in Investigations of Infra-Red Spectra.[77][78][79]

William Coblentz

1917: developed the thallous sulfide detector, which helped produce the first infrared search and track device able to detect aircraft at a range of one mile (1.6 km).

Theodore Case

1935: Lead salts – early missile guidance in .

World War II

1938: predicted that the pyroelectric effect could be used to detect infrared radiation.[80]

Yeou Ta

1945: The "Vampir" infrared weapon system was introduced as the first portable infrared device for military applications.

Zielgerät 1229

1952: grew synthetic InSb crystals.

Heinrich Welker

1950s and 1960s: Nomenclature and radiometric units defined by , G. J. Zissis and R. Clark; Robert Clark Jones defined D*.

Fred Nicodemenus

1958: (Royal Radar Establishment in Malvern) discovered IR detection properties of Mercury cadmium telluride (HgCdTe).[81]

W. D. Lawson

1958: and Sidewinder missiles were developed using infrared technology.

Falcon

1960s: and his colleagues at Honeywell Research Center demonstrate the use of HgCdTe as an effective compound for infrared detection.[81]

Paul Kruse

1962: demonstrated pyroelectric detection.[82]

J. Cooper

1964: W. G. Evans discovered infrared thermoreceptors in a pyrophile beetle.

[52]

1965: First IR handbook; first commercial imagers ( (now part of FLIR Systems Inc.)); Richard Hudson's landmark text; F4 TRAM FLIR by 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.

Barnes, Agema

1970: and George E. Smith proposed CCD at Bell Labs for picture phone.

Willard Boyle

1973: Common module program started by NVESD.

[83]

1978: Infrared imaging astronomy came of age, observatories planned, on Mauna Kea opened; 32 × 32 and 64 × 64 arrays produced using InSb, HgCdTe and other materials.

IRTF

2013: On 14 February, researchers developed a that gives rats the ability to sense infrared light, which for the first time provides living creatures with new abilities, instead of simply replacing or augmenting existing abilities.[84]

neural implant

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 Royal Society of London. Herschel used a 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".[63][64] The term "infrared" did not appear until late 19th century.[65] An earlier experiment in 1790 by Marc-Auguste Pictet demonstrated the reflection and focusing of radiant heat via mirrors in the absence of visible light.[66]


Other important dates include:[26]

Archived 2007-08-07 at the Wayback Machine (Omega Engineering)

Infrared: A Historical Perspective

Archived 2008-05-22 at the Wayback Machine, a standards organization for infrared data interconnection

Infrared Data Association

Archived 2011-10-13 at the Wayback Machine

SIRC Protocol

Archived 2011-07-19 at the Wayback Machine

How to build a USB infrared receiver to control PC's remotely

: detailed explanation of infrared light. (NASA)

Infrared Waves

Herschel's original paper from 1800 announcing the discovery of infrared light

Archived 2013-06-11 at the Wayback Machine, collection of thermogram

The thermographic's library

Archived 2015-12-22 at the Wayback Machine at ColourLex

Infrared reflectography in analysis of paintings

Molly Faries, Archived 2015-12-22 at the Wayback Machine, in Scientific Examination of Art: Modern Techniques in Conservation and Analysis, Sackler NAS Colloquium, 2005

Techniques and Applications – Analytical Capabilities of Infrared Reflectography: An Art Historian s Perspective