Abstract
Infrared radiation (IR) is electromagnetic radiation with wavelengths between 0.7 μm and 100 μm. It extends from visible light to THz waves. Because fundamentally different phenomena can be observed within the IR region, four sub-bands are usually distinguished: near-IR (NIR), mid-wave-IR (MWIR), long-wave-IR (LWIR) and very long-wave-IR (VLWIR). Although somewhat different definitions exist in literature, wavelengths from 0.7 μm to 2.5 μm belong to NIR, from 2.5 μm to 8 μm belong to MWIR, from 8 μm to 14 μm belong to LWIR and wavelengths above 14 μm belong to VLWIR. The IR photon energies range from 1.77 eV for 0.7 μm photons to 0.0124 eV for 100 μm photons.
The significance and practical applications of IR detectors are related to two distinct phenomena: emission of electromagnetic waves by all objects at T > 0 K and interaction of electromagnetic waves with vibrational modes of molecular bonds. Thermal imaging and molecular spectroscopy are, respectively, the two major fields that critically depend on the ability to detect IR radiation.
