How do photomultipliers work?
A photomultiplier tube, useful for light detection of very weak signals, is a photoemissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photocathode exposed to a photon flux.
What is PMT in physics?
Photomultiplier tubes (PMTs), also known as photomultipliers, are remarkable devices. While a PMT was the first device to detect light at the single-photon level, invented more than 80 years ago, they are widely used to this day, particularly in biological and medical applications.
What is a PMT detector?
PMT is the technology state of the art at present. The photomultiplier is an extremely sensitive light detector providing a current output proportional to light intensity. Photomultipliers are used to measure any process which directly or indirectly emits light.
How do Dynodes work?
A dynode is an electrode in a vacuum tube that serves as an electron multiplier through secondary emission. Secondary emission occurs at the surface of each dynode. Such an arrangement is able to amplify the tiny current emitted by the photocathode, typically by a factor of one million.
How many Dynodes are used in photomultiplier tube?
When a photon strikes the photocathode of the PMT, an electron is released, and the electron is directed toward the first of 10 dynodes by the bias voltage. At successive dynodes, each incoming electron ejects three or four more electrons, causing a multiplication of the current.
What is Photocathode made of?
Photocathodes are typically made of alkali-metal films such as potassium bromide (KBr), cesium telluride (CsTe), cesium iodide (CsI), or rubidium telluride (RbTe).
What are Dynodes in PMT?
In a PMT, dynodes are electrodes in a vacuum tube that serve as an electron multiplier through SEE (see Figure 1). The dynodes are so arranged that the electric fields between them cause the electrons emitted by each dynode to strike the next with an energy of a few hundred eV.
What is PMT in flow cytometry?
The most commonly used detectors for flow cytometry are the photomultiplier tubes (PMT) that reside in each channel of the instrument (Figure 1). In addition to converting the photons to photocurrent, the PMT amplifies the signal, a process that requires the application of a steady-state voltage to the detector.
Where are photomultipliers used?
Photomultipliers are used in research laboratories to measure the intensity and spectrum of light-emitting materials such as compound semiconductors and quantum dots. Photomultipliers are used as the detector in many spectrophotometers.
How many dynodes are used in photomultiplier?
For example, if at each stage an average of 5 new electrons are produced for each incoming electron, and if there are 12 dynode stages, then at the last stage one expects for each primary electron about 512 ≈ 108 electrons. This last stage is called the anode.
What are dynodes coated with?
A discrete dynode detector consists of an array of discrete dynode multipliers, usually containing 15–18 dynodes, coated with a metal oxide that has high secondary electron emission properties.
What was the first electrostatic photomultiplier ever made?
Electrostatic photomultiplier, a kind of photomultiplier tube demonstrated by Jan Rajchman of RCA Laboratories in Princeton, NJ in the late 1930s which became the standard for all future commercial photomultipliers. The first mass-produced photomultiplier, the Type 931, was of this design and is still commercially produced today.
How does the electron multiplier in a photocathode work?
The electron multiplier consists of a number of electrodes called dynodes. Each dynode is held at a more positive potential, by ≈100 Volts, than the preceding one. A primary electron leaves the photocathode with the energy of the incoming photon, or about 3 eV for “blue” photons, minus the work function of the photocathode.
What are the different types of photomultipliers?
Kinds of photomultiplier include: Photomultiplier tube, a vacuum tube converting incident photons into an electric signal. Silicon photomultiplier, a solid-state device converting incident photons into an electric signal.
Who was the inventor of the photomultiplier tube?
Magnetic photomultiplier, developed by the Soviets in the 1930s. Electrostatic photomultiplier, a kind of photomultiplier tube demonstrated by Jan Rajchman of RCA Laboratories in Princeton, NJ in the late 1930s which became the standard for all future commercial photomultipliers.