Photomultiplier tubes (photomultipliers or PMTs for short) are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum. They are members of the class of vacuum tubes, more specifically vacuum phototubes. These detectors multiply the current produced by incident light by as much as 100 million times or 108 (i.e., 160 dB), in multiple dynode stages, enabling (for example) individual photons to be detected when the incident flux of light is low.
Photomultiplier
Dynodes inside a photomultiplier tube
Fig. 2: Typical photomultiplier voltage divider circuit using negative high voltage.
Internal metallisation as a protective screen against unwanted lights sources
A vacuum tube, electron tube, valve, or tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
Later thermionic vacuum tubes, mostly miniature style, some with top cap connections for higher voltages
Hot tubes in an audio power amplifier, emitting their distinctive red-orange glow
Illustration representing a primitive triode vacuum tube and the polarities of the typical DC operating potentials. Not shown are the impedances (resistors or inductors) that would be included in series with the C and B voltage sources.
Radio station signal generator with vacuum tubes
