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Short-wavelength infrared SWIR, IR-B DIN: 1.4–3 μm 100–214 THz 413–886 meV 2,070–966 K (1,797–693 °C) 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 (see transmission windows). Mid-wavelength infrared MWIR, IR-C DIN; MidIR. [22]
An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation sometimes called black-body radiation emitted by the object being measured. They are sometimes called laser thermometers as a laser is used to help aim the thermometer, or non-contact thermometers or temperature guns , to describe the ...
The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far-infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14,000–4,000 cm −1 (0.7–2.5 μm wavelength) can excite overtone or combination modes of molecular vibrations .
The wavelength range from approximately 200 μm up to a few mm is often referred to as Submillimetre astronomy, reserving far infrared for wavelengths below 200 μm. Mid-infrared, from 30 THz to 120 THz (10–2.5 μm).
The reason for this has to do with the mechanical tolerance needed for good optical performance, which is related to the wavelength of the light being used. For the relatively long wavelengths of the far infrared, ~10 μm tolerances are adequate, whereas for the rock-salt region tolerances have to be better than 1 μm.
To allow mid-infrared observations within the JWST, the MIRI instrument has an additional cooling system. It works roughly similar to how most refrigerators or an air-conditioner works: a fluid is brought down to a cold temperature in the warm section, and sent back to the cold section where it absorbs heat, then it goes back to the condenser.