farinfrared

Far-infrared (FIR) is the portion of the infrared spectrum with wavelengths roughly from 25 to 350 micrometers, occasionally extended to about 1000 micrometers in some definitions. It lies beyond the mid-infrared and toward the submillimeter range, overlapping with the microwave region at its long end. Photon energies in this band are low, on the order of a few millielectronvolts. The radiation is strongly emitted by objects at relatively cold temperatures, roughly 15 to 100 kelvin.

Because Earth's atmosphere absorbs strongly in many far-infrared bands due to water vapor and carbon dioxide, observations are challenging; ground-based observations require high, dry sites or airborne and space platforms. Space telescopes and airborne observatories have been crucial for mapping cold dust in the interstellar medium, star-forming regions, and distant galaxies. Notable missions and facilities have covered portions of the FIR and adjacent submillimeter range, including space-based observatories such as ISO and Herschel, and instruments on space and airborne platforms.

Detectors used in the far-infrared include bolometers, superconducting transition-edge sensors, and kinetic inductance detectors, often cooled to cryogenic temperatures to achieve high sensitivity. Because of weak signals and atmospheric opacity, FIR instrumentation emphasizes sensitivity, low noise, and broad spectral coverage. FIR observations are essential for studying thermal dust emission, the structure of the interstellar medium, and the earliest stages of galaxy evolution.

In industry and applied imaging, far-infrared technology is used in thermal cameras for process monitoring and quality control, and in heating applications where long-wavelength radiation interacts with materials more deeply. Some consumer products promote health benefits linked to FIR exposure, but robust scientific evidence for such claims remains limited.