ABSTRACT
This chapter describes the basic features of various kinds of direct detectors used in the part of the spectrum – bolometers, kinetic inductance detectors, and photoconductors – and considers the pros and cons of different ways of coupling the telescope beam to the detectors. The cross-over region between the suitability of coherent and incoherent detection is typically in the submillimetre region but depends strongly on the exact application and requirements, and there are circumstances in which either technique can be used. Infrared and submillimetre detectors are operated at ultra-low temperatures inside cryogenic systems. The development of compact and reliable ultra-cold refrigeration systems means that the bolometric detectors in modern ground-based and space-borne instruments are usually operated at sub-kelvin temperatures. Both ground-based and space-borne observatories are used in the far-infrared to millimetre range. Transition edge superconducting detectors are easier to fabricate than semiconductor bolometer arrays because they can be made using standard lithographic techniques.
