ABSTRACT
The use of thermal detectors for IR (infrared) imaging has been the subject of research and development for many decades. These devices achieved their fundamental limits of performance by about 1970. Thermal detectors are not useful for high-speed scanning thermal imagers. However, the speed of thermal detectors is quite adequate for nonscanned imagers with 2D detectors. Figure 25.1 shows the dependence of noise equivalent difference temperature (NEDT) on noise bandwidth for typical detectivities of thermal detectors [1]. The calculations have been carried out assuming 100 × 100 μm2 pixel size, 8–14 μm spectral range, f/1 optics, and t op = 1 of the IR system. With large arrays of thermal detectors, the best values of NEDT below 0.1 K could be reached because effective noise bandwidths less than 100 Hz can be achieved. This compares with a bandwidth of several hundred kilohertz for conventional cooled thermal imagers with a small photon detector array and scanner. Realization of this fact caused a new revolution in thermal imaging. This is due to the development of 2D electronically scanned arrays in which moderate sensitivity can be compensated by a large number of elements. Large-scale integration (LSI) combined with micromachining has been used for manufacturing large 2D arrays of uncooled IR sensors. This enables fabrication of low-cost and high-quality thermal imagers.
