IRFPA detectors

The newest and perhaps most versatile of the detectors shown is the QWIP array. QWIP detectors are made from gallium arsenide (GaAs) material. These detectors are narrow-band, high-speed, high-sensitivity detectors that can be designed to operate in selected narrow bands from the MWIR (2-5 pm) to the LWIR (8-14 pm). The versatility of this detector, as well as others, will be illustrated in the applications chapters in Part II of this text. 

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High-resolution thermal imagers featuring IRFPA detectors have eompletely replaced opto-mechanically scanned imagers, and at this writing, virtually all commercially marketed IR cameras feature IRFPA detectors. 

Spatial resolution 1.2-1.6 milliradian (776 x 484 near IRFPA detector)... 

Uncooled long-wave IRFPA cameras were developed in the mid-1990s. These featured uncooled microbolometric and ferroelectric detector arrays (8-14 pm). 

Figure 2.20 is a schematic diagram of an IRFPA camera based on bolometric IR detectors. 

Modem IRFPA thermal imagers provide quantitative temperature measuring capability and high resolution image quality. Detector cooling is sometimes required and this is most often accomplished by means of a thermoelectric, or Peltier effect, cooler or an electric-powered Stirling-cycle nitrogen or helium cooler. 

While the individual thermal detector elements are slow in response, on the order of milliseconds, every one of the thousands of elements in the array is always exposed to the incoming target radiation, and fast enough to respond fully to a typical 30-Hz video scanning rate. Initially offered to the security and law enforcement market, these imagers continue to find their way into a wide variety of commercial and industrial applications. Because these instruments have no measurement capabilities, they are appropriately classified as thermal viewers. See Sec 4.3.3.2 for a discussion of measuring IRFPA cameras. 

Focal plane array (FPA) - A linear or two-dimensional matrix of detector elements, typically used at the focal plane of an instrument. In thermography, rectangular FPAs are used in staring (non-scanning) infrared imagers. These are called IRFPA imagers. 

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