Infrared

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means "below red" (from the Latin infra, "below"), red being the color of visible light of longest wavelength. Infrared radiation spans three orders of magnitude and has wavelengths between 700 nm and 1 mm.

Different regions in the infrared

IR is often subdivided into:

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• near infrared NIR, IR-A DIN, 0.7–1.4 µm in wavelength, defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO₂ glass (silica) medium.
• short wavelength IR SWIR, IR-B DIN, 1.4–3 µm, water absorption increases significantly at 1450 nm
• mid wavelength IR MWIR, IR-C DIN, also intermediate-IR (IIR), 3–8 µm
• long wavelength IR LWIR, IR-C DIN, 8–15 µm)
• far infrared FIR, 15–1000 µm

However, these terms are not precise, and are used differently in various studies i.e. near (0.7–5 µm) / mid (5–30 µm) / long (30–1000 µm). Especially at the telecom-wavelengths the spectrum is further subdivided into individual bands, due to limitations of detectors, amplifiers and sources. Infrared radiation is often linked to heat, since objects at room temperature or above will emit radiation mostly concentrated in the mid-infrared band (see black body).

Related Topics:
Heat - Emit radiation - Black body

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The common nomenclature is justified by the different human response to this radiation (near infrared = the red you just cannot see, far IR = thermal radiation), 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 1050 nm, while InGaAs sensitivity starts around 950 nm and ends between 1700 and 2200 nm, depending on the specific configuration). Unfortunately the international standards for these specifications are not currently available.

Related Topics:
Silicon - InGaAs

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