In the NIR and SWIR range different portions are absorbed, which in combination enables a precise determination to be made. Credit Simola et al., ACS Photonics 2021, 8, 7, 2166-2173 (CC BY-NC-ND 4.0) ...

These FPAs are usually made of silicon, as silicon-based sensors are sensitive in the visible and part of the near-infrared spectrum. For wavelengths beyond near infrared, more exotic materials ...