Photoelectric photometry
H. J. J. Braddick · Reports on Progress in Physics · 1960
The development of photoelectric devices has occasioned considerable changes in all types of instrument in which intensities are measured or compared. These devices are directly sensitive to flux and the optical systems used with them must be designed accordingly. At very low intensities the photomultiplier cell allows a light flux of only a few quanta per second to be measured and the theoretical limitations and practical arrangements are discussed. In the ultra-violet spectrum, the photoelectric technique must be revised, but efficient detectors for the whole region are known and some are described. Infra-red detection requires recourse to the `internal' photoelectric effect in semiconductors, and the properties of the most important detectors of the class are briefly described. A characteristic advantage of photoelectric detectors is that their output is linearly related to the intensity of the incident light and is in a form suitable for electronic data processing by analogue or digital methods. Some examples in industrial and astronomical photometry which make use of this property are described, and there are some notes on precision photo-electric photometry as used in the maintenance and use of standards of radiation.