The principle of photon type detector

Photon-type detectors made using the external photoelectric effect are vacuum electronic devices such as phototubes, photomultiplier tubes, and infrared transducers. These devices contain a photoelectric cathode that is sensitive to photons, and when photons are projected onto the photoelectric cathode, the photons may be absorbed by the electrons in the photoelectric cathode, and the electrons that gain a large enough energy can escape the photoelectric cathode and become free photoelectrons. In a photomultiplier tube, photoelectrons move under the action of a positively charged anode, constituting a photocurrent. The difference between a photomultiplier tube and a phototube is that between the photocathode and the anode of the photomultiplier tube, a number of electrodes are set up that rise in potential step by step and produce secondary electrons (called the striking electrodes). Photoelectrons escaping from the photocathode in the hit to take the pole voltage accelerated by the collision with the hit to take the pole, the multiplier effect occurs, and finally form a larger photocurrent signal. Therefore, the photomultiplier tube has a much higher sensitivity than the photocell. Infrared tube is a kind of infrared - visible image converter, it consists of photoelectric cathode, anode and a simple electronic optical system. Photoelectrons are accelerated by the anode while being focused by the electro-optical system, and when they impact on the phosphorescent screen connected to the anode, a green light image signal is emitted.