Why Signal To Noise Matters In SWIR Imaging

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For a long time, Short Wave Infrared (SWIR) imagers were not commonly used for inspection. It was difficult to conceive of using a SWIR camera to inspect something with non-visible light that one cannot see with one's own eyes.

SWIR is often defined as a band of light from 900-1700nm because that is the standard detection range for Indium Gallium Arsenide (InGaAs) detectors, but technically the SWIR band is from 1100-2600nm. With InGaAs detectors, the short wavelengths turn on at 900nm. Any light shorter than 900nm is absorbed by Indium Phosphide (InP), the substrate material that the InGaAs detector material is grown on. InGaAs material turns off at 1700nm because of the chemical structure of In Ga As (the exact structure for InGaAs). Newer SWIR cameras, like Princeton Infrared Technologies’ (PIRT) imagers, have the InP substrate removed to allow detection to start at 400nm. There are also extended InGaAs detectors that image all the way up to 2600nm, but these have much higher noise, require cooling and are significantly more expensive.