Written by Kevin Tavolaro
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A photomultiplier tube, or "PMT" is a component that regulates interaction between electrons and light. PMTs are used in many electrical applications requiring a graphic output of some sort. This can include the detailed photo-realism of a television, the graphic interface of a computer monitor, or the simple, yet consistently reliable and efficient monochrome readings on an oscilloscope. All of these devices use a PMT, which is a specialized type of vacuum tube, to detect and react to light caused by electron input. This includes ultraviolet and infrared transmissions, as well as standard visible light.

There are several reasons for the continued popularity of photomultiplier tubes, despite the fact that they are one of the oldest components in electrical transmission. Computer science, medicine, and other high tech fields like astronomy and oceanography rely on photomultiplier tubes to provide their equipment with quick, reliable visual data readouts. PMTs are lightweight, make little noise, and are highly efficient when used in certain situations. In addition, they posses an exceedingly high frequency response level, which makes them the best candidate for many applications.

PMT Components

A PMT is divided into several sections, each of which facilitates a different stage of transmission. As photons are released into first section, the cathode and electrons are generated. The cathode then projects these electrons onto the surface of the dynode. The surface of the dynode reflects the electrons, which causes them to collide with each other. The collisions between electrons serve to amplify them, which rapidly escalates the velocity. This is known as the photoelectric effect.

The increased velocity of the electrons in this situation generates a rise in intensity. When the intensity reaches a level dictated by the source, they produce a steady signal. The signal is transmitted from the dynode to the final section of the PMT, the anode. Because of the elevated frequency level possible in the photoelectric process, a single photon is capable of generating all of this activity so far. The anode then takes the beam, generated by a single photon, and transmits it as one component of a graphical output that can be observed on a monitor, screen, scope, or other viewing device, depending on the complexity of the image.

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