The mission of Episensors™ is to develop, make, and sell high-performance, low cost infrared cameras including HgCdTe-based extended short wavelength infrared (eSWIR) cameras. Episensors™ is currently marketing the “Night SWEEP” family of infrared cameras for defense and commercial applications.
Short Wave Infrared Overview
Short wave infrared (SWIR) sensing technology is useful in a variety of military and civilian applications, and provides significant advantages over conventional low-light level imaging. The presence of nightglow in the SWIR spectrum can provide a significant amount of ambient signal both during day and night, allowing these types of imaging systems to operate without a secondary illumination source under most field conditions. Episensors™ is leveraging recent advances in HgCdTe detector technology to reduce the size, weight and power consumption of SWIR camera systems, and to extend the cutoff wavelength from the conventional 1.7 micron cutoff up to a 2.5 or 3.0 micron cutoff. Extending the operating wavelength range allows the camera to capture more night glow for enhanced low light imaging, and provides additional spectra for covert communication applications.
Advantages of SWIR Imaging
Light in the short-wave infrared (SWIR) spectrum (namely wavelengths of approximately 1.0 to 3.0 microns) can be seen through fog, haze, dust, light dirt and other adverse visual conditions both during the day and at night. Portions of the SWIR spectrum will pass through glass, providing a significant advantage over mid-wave and long-wave infrared imaging. SWIR light is also capable of reflection and absorption by objects, thus enabling strong contrasts and high resolution imaging. SWIR illumination comes from the sun during the day and atmospheric nightglow at night; in particular, it permits passive imaging during the night without starlight or moonlight illumination. Light in other parts of the infrared spectrum (for instance in the mid-wavelength and long wavelength regions) are emitted by objects rather than reflected by them, which allows only for thermal imaging of objects radiating heat against a cool background and may not provide the sharp contrast necessary for precise identification. SWIR cameras image reflected SWIR radiation coming from the sky, which produces an image similar to the visible light images our eyes are used to looking at and analyzing. Thus, cameras that can image in the SWIR have a significant advantage over competitors because such cameras can provide high-resolution imaging in the presence of visual obscurants, both at day and at night.
What is eSWIR?
The wavelength range comprising the SWIR spectrum is 1.0-3.0 microns. However, conventional commercially-available SWIR cameras utilizing InGaAs detector technologies can only image well at wavelengths up to 1.7 microns, leaving a wavelength gap in the SWIR, namely wavelengths longer than 1.7 microns. A SWIR camera that can see beyond 1.7 microns (such as a camera using a HgCdTe focal plane array) is referred to as an “extended” SWIR (eSWIR) camera. Roughly half of the available SWIR emission from the sky at night falls between 1.7-2.5 microns, which means that a camera that is capable of eSWIR imaging will produce a higher quality image than a standard SWIR camera.
Night SWEEP eSWIR Video Comparison Using a HgCdTe Focal Plane Array
The video immediately below is taken at the 1.0-1.7 micron wavelength range, which is the conventional range for SWIR cameras. Auto-gain is off.
The video immediately below is taken at the 1.7-2.5 micron wavelength range, which is the extended SWIR range. Auto-gain is off.
The video immediately below is taken at the full 1.0 - 2.5 micron wavelength range, which is the full range of a Night SWEEP camera. Notice that the amount of flux in this image is much greater than in either image above because it combines the flux from both. The combination of flux from both ranges enhances the signal available for imaging.
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