The detection of sub-mm radiation

The characteristics of an ideal detector are discussed and are compared with the practical results achieved with the following types of detectors: superheterodyne and video receivers using point-contact rectifiers; InSb photoconductive detectors, both wide-band and tunable; thermal detectors, including the Golay cell, and carbon, germanium and superconducting tin bolometers. The practical performance achieved is considerably inferior to that which is ideally possible. The extension of microwave techniques is limited by practical difficulties in constructing the detectors and other components required, but the performance obtained from the infra-red systems which require cooling with liquid helium is limited by that of the LF amplifiers used with them.