A solar blind photocathode can be manufactured so as to have excellent sensitivity to ultraviolet light, but no response to daylight. Such cathodes are useful for flame detection, especially for flames such as those created by burning hydrogen in which no visible light is emitted. Applications for devices having sensitivity in the infrared are now only under development. One that is of great interest is the detection of the very weak emission from singlet oxygen. Singlet oxygen is a highly reactive compound believed to play an important role in the destruction of brain cells immediately after a stroke and in the photochemical damage of plastics and other organic compounds that are exposed to sunlight or ultraviolet radiation.
All photocathodes produce an electron by the photoelectric effect.
This photoelectron is very difficult to detect. It needs to be amplified by factors of a hundred thousand or a million before it can be processed. This can be done inside the PMT without the need for external amplifiers. This amplification is carried out using the dynode chain. The dynodes are a series of 8 to 12 metal plates.