By MARC HANSEN
The military and industrial communities are investigating shortwave infrared (SWIR) technology for new and improved imaging solutions for a variety of challenging applications. Indium gallium arsenide (InGaAs) is a material often used for SWIR imaging due to its high quantum efficiency and low dark current. This advanced InGaAs material makes these detectors the most sensitive imagers that operate in the shortwave IR wavelength range at any given temperature. A standard InGaAs camera responds to wavelengths from about 0.9 µm to 1.7 µm, utilizing reflected radiation to produce images that resemble those from a black and white visible-response camera. Since SWIR imagers are capable of creating high-contrast, high-resolution imagery well beyond the visible spectrum, the performance of the cameras is often dictated by the lenses chosen for the application.
InGaAs cameras can use standard off-the-shelf visible lenses due to the fact that SWIR wavelengths readily pass through glass. This is in contrast to mid-wave IR (MWIR 3 µm to 5 µm) and long-wave IR (LWIR > 7 µm) cameras that require exotic and expensive lens materials. Even though a visible lens can produce impressive results when imaging in the SWIR, only a lens assembly designed and optimized specifically for the shortwave infrared wavelength will be able to take full advantage of the camera performance. With this newly emerging lens market, some manufacturers have produced SWIR lenses at a premium price to capitalize on the industry's quest for higher performance.