The definition of "infrared" is nuanced, as in extreme circumstances the human eye can detect wavelengths of light deep into the NIR band. Numbers between 700 and 800 nm are typically used as the cutoff wavelength. | Division | Abbr | Wavelength | Frequency | | ------------------ | --------------- | ------------------- | ----------- | | Near-Infrared | NIR, IR-A | 750-1,400 nm | 214-400 THz | | Shortwave Infrared | SWIR, IR-B | 1,400-3,000 nm | 100-214 THz | | Midwave Infrared | MWIR, IR-C, IIR | 3,000-8,000 nm | 37-100 THz | | Longwave Infrared | LWIR, IR-C | 8,000-15,000 nm | 20-37 THz | | Far Infrared | FIR | 15,000-1,000,000 nm | 0.3-20 THz | \* NIR & SWIR are considered reflective non-emissive infrared and while materials fully absorb them, while MWIR and LWIR are considered emissive thermal infrared as all materials not at absolute zero emit light at these wavelengths. # Bands ## Near Infrared > Goes up to the wavelength of the first water absorption band, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum; examples include night vision devices such as night vision goggles. Near-infrared spectroscopy is another common application. ## Short-Wavelength Infrared > 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 also: [[#Optical Telecommunications]] ## Mid-Wavelength Infrared > In guided missile technology the 3–5 μm portion of this band is the atmospheric window in which the seekers of passive IR 'heat seeking' missiles are designed to work, homing on to the Infrared signature of the target aircraft, typically the jet engine exhaust plume. This region is also known as thermal infrared. ## Long-Wavelength Infrared > The "thermal imaging" region, in which sensors can obtain a completely passive image of objects only slightly higher in temperature than room temperature – for example, the human body – based on thermal emissions only and requiring no illumination such as the sun, moon, or infrared illuminator. This region is also called the "thermal infrared". ## Far Infrared # Uses ## Thermography and Pyrometry IR can be used to accurately determine the surface temperature of objects if the emissivity of the objects are known. If an object becomes hot enough, they will begin to emit radiation in the visible light spectrum as well. # Characteristics ## Emissivity A material's deviation from the emissive spectra of the ideal black body is its emissivity. While this can be used to help determine a material's composition at a great distance, it is also a barrier to using emissive spectra to ascertain the temperature of unknown materials based purely on their emission spectra. # Standards > Infrared radiation is generally considered to begin with wavelengths longer than visible by the human eye. There is no hard wavelength limit to what is visible, as the eye's sensitivity decreases rapidly but smoothly, for wavelengths exceeding about 700 nm. Therefore wavelengths just longer than that can be seen if they are sufficiently bright, though they may still be classified as infrared according to usual definitions. Light from a near-IR laser may thus appear dim red and can present a hazard since it may actually be quite bright. And even IR at wavelengths up to 1,050 nm from pulsed lasers can be seen by humans under certain conditions. ## CIE Specification | Abbreviation | Wavelength | Frequency | | ------------ | ----------------------------------------- | ----------------- | | IR-A | 780 nm – 1,400 nm <br>(0.78 μm – 1.4 μm) | 215 THz – 430 THz | | IR-B | 1,400 nm – 3,000 nm <br>(1.4 μm – 3 μm) | 100 THz – 215 THz | | IR-C | 3,000 nm – 1 mm <br>(3 μm – 1,000 μm) | 300 GHz – 100 THz | ## ISO 20473 Specification | Designation | Abbreviation | Wavelength | | ------------- | ------------ | ----------- | | Near-Infrared | NIR | 0.78–3 μm | | Mid-Infrared | MIR | 3–50 μm | | Far-Infrared | FIR | 50–1,000 μm | ## Astronomic Usage | Designation | Abbreviation | Wavelength | | ------------- | ------------ | ------------- | | Near-Infrared | NIR | 0.7 to 2.5 μm | | Mid-Infrared | MIR | 3 to 25 μm | | Far-Infrared | FIR | above 25 μm. | These are generalizations used in astronomy. There are more specific photometric systems which break down each region from ultraviolet to mid-infrared into sometimes many smaller sections. ## Sensor Response | Designation | Abbr | Wavelength | Detector | | ------------------ | ----- | ----------------------- | ------------------------ | | Near-Infrared | NIR | 0.7 to 1 μm | | | Short-Infrared | SWIR | 1 to 3 μm | `InGaAs`, Cyro `HgCdTe` | | Mid-Infrared | MWIR | 3 to 5 μm | `InSb`, `HgCdTe`, `PbSe` | | Long-Infrared | LWIR | 8 to 12 (or 7 to 14) μm | `HgCdTe` | | Very-Long-Infrared | VLWIR | 12 to 39 μm | Doped Silicon | This break down is based on the response of various chemical detectors. Again, not a standard, just common parlance. ## Optical Telecommunications | Band | Descriptor | Wavelength range | | ------ | -------------------- | ---------------- | | O band | Original | 1,260–1,360 nm | | E band | Extended | 1,360–1,460 nm | | S band | Short wavelength | 1,460–1,530 nm | | C band | Conventional | 1,530–1,565 nm | | L band | Long wavelength | 1,565–1,625 nm | | U band | Ultralong wavelength | 1,625–1,675 nm | # References - https://en.wikipedia.org/w/index.php?title=Infrared - https://en.wikipedia.org/w/index.php?title=Photometric_system - https://www.youtube.com/watch?v=XHDXk9THJZM