264:(VOx, pronounced "Vox"). A variety of lead salts can also be used, but are less common today. None of these materials can be grown into crystals anywhere near the size of modern silicon crystals, nor do the resulting wafers have nearly the uniformity of silicon. Furthermore, the materials used to construct arrays of IR-sensitive pixels cannot be used to construct the electronics needed to transport the resulting charge, voltage, or resistance of each pixel to the measurement circuitry. This set of functions is implemented on a chip called the
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similar fashion to a scanning array except that it images perpendicularly to the motion of the camera. A staring array is analogous to the film in a typical camera; it directly captures a 2-D image projected by the lens at the image plane. A scanning array is analogous to piecing together a 2D image with photos taken through a narrow slit. A TDI imager is analogous to looking through a vertical slit out the side window of a moving car, and building a long, continuous image as the car passes the landscape.
307:(PRNU). When un-illuminated, each pixel has a different "zero-signal" level, and when illuminated the delta in signal is also different. This non-uniformity makes the resulting images impractical for use until they have been processed to normalize the photo-response. This correction process requires a set of known characterization data, collected from the particular device under controlled conditions. The data correction can be done in software, in a
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Scanning arrays were developed and used because of historical difficulties in fabricating 2-D arrays of sufficient size and quality for direct 2-D imaging. Modern FPAs are available with up to 2048 x 2048 pixels, and larger sizes are in development by multiple manufacturers. 320 x 256 and 640 x 480
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imagers in that they image the desired field of view without scanning. Scanning arrays are constructed from linear arrays (or very narrow 2-D arrays) that are rastered across the desired field of view using a rotating or oscillating mirror to construct a 2-D image over time. A TDI imager operates in
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in the visible spectrum. FPAs operate by detecting photons at particular wavelengths and then generating an electrical charge, voltage, or resistance in relation to the number of photons detected at each pixel. This charge, voltage, or resistance is then measured, digitized, and used to construct an
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A peculiar aspect of nearly all IR FPAs is that the electrical responses of the pixels on a given device tend to be non-uniform. In a perfect device every pixel would output the same electrical signal when given the same number of photons of appropriate wavelength. In practice nearly all FPAs have
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The difficulty in constructing high-quality, high-resolution FPAs derives from the materials used. Whereas visible imagers such as CCD and CMOS image sensors are fabricated from silicon, using mature and well-understood processes, IR sensors must be fabricated from other, more exotic materials
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or related weapons guidance sensors, infrared astronomy, manufacturing inspection, thermal imaging for firefighting, medical imaging, and infrared phenomenology (such as observing combustion, weapon impact, rocket motor ignition and other events that are interesting in the infrared spectrum).
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and between the FPA’s internal conductors. By replacing the receiver in the breadboard for one with a shorter focal length, the focus of the collimator was reduced and the system’s threshold for signal recognition was increased. This facilitated a better image by cancelling cross talk.
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Itzler, Mark A.; Entwistle, Mark; Owens, Mark; Patel, Ketan; Jiang, Xudong; Slomkowski, Krystyna; Rangwala, Sabbir; Zalud, Peter F.; Senko, Tom (2010-08-19). Dereniak, Eustace L; Hartke, John P; Levan, Paul D; Sood, Ashok K; Longshore, Randolph E; Razeghi, Manijeh (eds.).
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Another method was to add a flat thinned substrate membrane (approximately 800 angstroms thick) to the FPA. This was reported to eliminate pixel-to-pixel cross talk in FPA imaging applications. In another an
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to collect and direct the breadboard’s laser beam onto individual pixels. Since low levels of voltage were still observed in pixels that did not illuminate, indicating that illumination was prevented by
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The low volumes, rarer materials, and complex processes involved in fabricating and using IR FPAs makes them far more expensive than visible imagers of comparable size and resolution.
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Marino, Richard M.; Stephens, Timothy; Hatch, Robert E; McLaughlin, Joseph L.; Mooney, James G.; O'Brien, Michael E.; Rowe, Gregory S.; Adams, Joseph S.; Skelly, Luke (2003-08-21).
187:. At optical and infrared wavelengths, it can refer to a variety of imaging device types, but in common usage it refers to two-dimensional devices that are sensitive in the
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Goldberg, A.; Stann, B.; Gupta, N. (July 2003). "Multispectral, Hyperspectral, and Three-Dimensional
Imaging Research at the U.S. Army Research Laboratory" (PDF).
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D., Gunapala, S.; V., Bandara, S.; K., Liu, J.; J., Hill, C.; B., Rafol, S.; M., Mumolo, J.; T., Trinh, J.; Z., Tidrow, M.; D., LeVan, P. (May 2005).
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because silicon is sensitive only in the visible and near-IR spectra. Infrared-sensitive materials commonly used in IR detector arrays include
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Marino, Richard M.; Davis, William Rhett (2004). "Jigsaw : A Foliage-Penetrating 3 D Imaging Laser Radar System".
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or bonded to the ROIC, typically using indium bump-bonding, and the resulting assembly is called an FPA.
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spectrum. Devices sensitive in other spectra are usually referred to by other terms, such as CCD (
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was reported with capabilities to repress cross talk between FPAs. Researchers at the
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would swamp the detected signal. Devices can be cooled evaporatively, typically by
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in the camera electronics, or even on the ROIC in the most modern of devices.
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consisting of an array (typically rectangular) of light-sensing pixels at the
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temperatures, and others (such as resistive amorphous silicon (a-Si) and VOx
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Proceedings of the
International Conference on International Fusion
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image of the object, scene, or phenomenon that emitted the photons.
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Detectors and
Imaging Devices: Infrared, Focal Plane, Single Photon
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both significant pixel-to-pixel offset and pixel-to-pixel
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295:(LN2) or liquid helium, or by using a
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260:(InGaAs, pronounced "Inn-Gas"), and
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216:Further information:
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106:August 2018
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377:collimator
369:breadboard
340:Cross talk
274:hybridized
179:is at the
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359:imaging.
281:cryogenic
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