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Concept
Far infrared
Summary
Far infrared (FIR) refers to a specific range within the infrared spectrum of electromagnetic radiation. It encompasses radiation with wavelengths ranging from 15 micrometers (μm) to 1 mm, which corresponds to a frequency range of approximately 20 THz to 300 GHz. This places far infrared radiation within the CIE IR-B and IR-C bands. The longer wavelengths of the FIR spectrum overlap with a range known as terahertz radiation. Different sources may use different boundaries to define the far infrared range. For instance, astronomers often define it as wavelengths between 25 μm and 350 μm. It is important to note that far infrared photons possess significantly lower energy compared to visible light photons, with tens to hundreds of times less energy.
Far-infrared astronomy
Objects within a temperature range of approximately 5 K to 340 K emit radiation in the far infrared range as a result of black-body radiation, in accordance with Wien's displacement law. This characteristic is utilized in the observation of interstellar gases, which are frequently associated with the formation of new stars.
An illustrative case is the brightness observed in far infrared images of the center of the Milky Way galaxy. This brightness arises from the high density of stars in that region, which heats the surrounding dust and induces radiation emission in the far infrared spectrum. Excluding the center of the Milky Way galaxy, the galaxy M82 is the most prominent far-infrared object in the sky, with its central region emitting amounts of far infrared light equivalent to the combined emissions of all the stars in the Milky Way. The source responsible for heating the dust at the center of M82 remains unknown.
Certain human proximity sensors utilize passive infrared sensing within the far infrared wavelength range to detect the presence of stationary and/or moving human bodies.
Researchers have observed that among all forms of radiant heat, only far-infrared radiation transfers energy solely in the form of heat that can be sensed by the human body.
Official source
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