shortwaveinfrared

Shortwave infrared (SWIR) refers to the portion of the infrared spectrum roughly from 1.0 to 3.0 micrometers. It lies between the near-infrared and mid-wave infrared bands and exploits atmospheric transmission windows that permit passive imaging in daylight and twilight. In practice, many SWIR systems cover about 1.0–2.6 or 2.0–2.5 micrometers, with some extended-range sensors reaching near 3 micrometers.

Detector technology for SWIR is dominated by indium gallium arsenide (InGaAs) sensors, which are sensitive from about 0.9 to 2.6 micrometers. Extended-range variants and alternative materials enable access to parts of the 2–3 micrometer region. SWIR cameras use focal plane arrays and can be uncooled or thermoelectrically cooled, with cooling improving noise performance for long exposures or high-sensitivity imaging. Optical materials and coatings for SWIR differ from visible optics, commonly involving fused silica for shorter wavelengths and materials such as ZnSe or CaF2 for longer wavelengths.

Imaging in the SWIR band offers advantages in hazy, smoky, or low-light conditions because many particles are more transparent at these wavelengths, and some materials exhibit distinct spectral signatures in SWIR. Water and moisture have characteristic absorption features near 1.4 and 1.9 micrometers, enabling material discrimination; vegetation and minerals also show unique SWIR reflectance profiles useful in remote sensing and geology.

Applications include security and surveillance, where passive SWIR cameras provide night-time imaging without illumination; industrial inspection of plastics, semiconductors, and packaging; agricultural monitoring; and scientific fields such as astronomy and remote sensing. Limitations include cost, the need for specialized optics and cooling for high performance, and the presence of strong atmospheric absorption bands at certain wavelengths.