In order to understand the future direction of infrared (IR) technology, it is meaningful to examine the road that it has already traveled. The earliest IR systems were developed in the 1960s and consisted of a limited number of elements of extrinsic photoconductors operating at very low temperatures. Images were obtained by the extremely rapid scanning of the IR scene over the small detector arrays. Power expenditures were high, and sensitivity was poor, but the capability to see in the dark was born, and the quest began for the development of ever-improving detector materials technologies and architectures that will ultimately allow for the detection of photons at room temperature in all IR spectral bands. In this chapter we will trace the evolution of the various generations of detector architectures over the years from 1960 to the present. It makes for an interesting journey.
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