Materials behave differently in different light wavelengths. Since SWIR imaging is similar to visible light imaging, just with different wavelengths, the idea is to find the contrast. SWIR imaging is a type of non-visible imaging. SWIR stands for shortwave infrared, which is a band of light just beyond human vision. It ranges from about 900 nm to 2300 nm. SWIR light transmits through silicon, so sensors for SWIR imaging typically use indium gallium arsenide(InGaAs) based detectors. "The SWIR wavelengths will get passed through silicon, so you can't make a SWIR sensor out of silicon," says Glen Ahearn, Sales Application Support Manager, Teledyne DALSA (Waterloo, ON, Canada; www. teledynedalsa.com). "One of the fundamental properties of a sensor is that it is struck by incoming photons that are absorbed at some layer in the silicon wafer, converted to electrons, and that charge is then stored in each pixel well on that sensor. To absorb the light and turn it into a charge and store that charge, you can't have the light passing directly through it. If the SWIR light is going to pass right through the silicon, you can't make your SWIR sensor out of silicon. InGaAs is material that will absorb the SWIR light, much like the silicon absorbs visible light, and it will convert it into a charge that is stored and then read out at the appropriate time."
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