This article outlines the most important sensors used in confocal microscopy. By confocal microscopy, we mean "True Confocal Scanning", i.e. the technique that illuminates and measures one single point only. The aim is not to impart in-depth specialist knowledge, but to give the user a small but clear overview of the differences between the various technologies and to advise on which sensor may be most suitable for which applications.
First, we shall give a brief description of the photomultiplier tube (PMT). Having established how light is converted into an electric signal, we shall go on to deal with different methods of primarily picking up this electric signal with the sensor. Basically, these methods apply equally to all sensors, although the suitability of the conversion techniques varies from sensor to sensor.
Finally, we describe the two recent sensor techniques deploying semiconductor technology (at least in part): the avalanche photo diode,