Photomultiplier (PMT) Tubes

A photomultiplier tube, or pmt tube, or photomultiplier is a light detector with high sensitivity, the photomultiplier tube converts light into electrons, accerates the electrons and multiplies the number of electrons at the dynodes and generate an amplified photocurrent at the output anode, and the current will often be transferred into a readable voltage pulse using a load resistor. Photomultiplier tubes are critical elements for the purpose of conversion of light signals into the forms of electrical signals, which can be further processed into digital signals and data that can be analyzed and monitored. PMTs stand out with their high sensitivity and capabilities to detect very weak light signals attributed to an avalanche multiplication process. Their larger active areas allow them to capture more light that might be diverging, which is a significant advantage over smaller-area detectors like avalanche photodetectors (APDs), which are less effective at capturing signals that are spread over a large area.

The basic working principle of the photomultiplier detector is the photoelectric effect. A photomultiplier tube consists of an optical window, a photocathode, a chain of dynodes, an enclosing vacuum envelope, and an output dynode. The optical window can be located at terminals of the vacuum tube; in this case, the photomultiplier tube is called a head-on PMT. When the optical window is located at the side of the vacuum tube, the photomultiplier is called a side-on PMT. Typical materials for manufacturing the optical windows of the PMT tubes include borosilicate glass, UV fused silica or magnesium fluoride. The optical window’s transmission wavelength range determines the shorter cut-off wavelength of the spectral response of the PMT.

The photocathode is a thin photosensitive film that absorbs light and releases photoelectrons. Its thickness and type govern the longer cut-off wavelength of the PMT’s spectral response. Different materials are used for light detection and signal conversion depending on the spectral characteristics of the input lights. For example, bialkali are used for the blue region and visible wavelengths, and multialkali offers expanded sensitivity into the NIR region. For PMT tubes designed for scintillators, as most scintillators emit blue light and green light, the luminous sensitivity (termed in µA/lm), which is the refers to how sensitive a PMT is to taking into the account of human visual perception measured for an incident flux of 1 lumen from a tungsten filament,  in addition to the blue sensitivity, also called luminous filtered sensitivity which describe the PMT’s efficiencies in detecting light in the blue region of the electromagnetic spectrum, termed in µA/lmF, are often used to define the spectral sensitivity of the photomultiplier tube instead of using responsitivities/radiant sensitivity quantified as generated photocurrent per watt of incident optical power. 

A vital specification that quantifies the how efficient a photomultiplier converts incident photons into detectable electrons at the cathode is the Quantum Efficiency (QE), which can be affected by a combination of multiple factors including the photocathode material, the wavelength of the incoming light, the transmission and thickness of the optical window, and the electron collection efficiencies. For applications using green-emitting scintillators, a more useful parameter is the integral quantum efficiency (IQE), defined as the integral product of the photocathode spectral sensitivity and the light emission spectrum. The photocathode can also influence the dark current, which is the unwanted current generated even without light input. 

These photoelectrons are then accelerated and directed towards a series of dynodes. A chain of multiple dynodes with potential differences arranged such that the potential of the previous dynode is higher than the next dynode (i.e. the voltages at each dynode gets more and more positive in succession). When an electron strikes a dynode, it knocks off more electrons, resulting in a cascade of electrons; the process is called secondary electron emission. The dynode chains are responsible for the amplification and multiplication of electrons. Gain, which refers to how much the initial photoelectron signal is multiplied as it travels through the dynodes, is related to dynode number, geometries and material, and the voltage supplies.

The anode is the electrode that collects the electrons that have been multiplied or accelerated through a process, generating a current proportional to the number of electrons collected, and this current is used as an output signal. The anode sensitivities, expressed in A/lm are a product of the product of cathode sensitivity, collection efficencies and gain.

Hangzhou Shalom EO offers stock and custom photomultiplier tubes (PMTs) designed for scintillation detectors. Our PMT tubes are optimised for applications in combination with scintillators. Our standard photomultiplier tubes contain borosilicate glass optical windows with outstanding transmission, bialkali photocathodes, dynode chains, output anodes, pin base and a vacuum envelope. The dynodes and anode adopt either a box and grid design to optimise the collection and amplification of photoelectrons and a box-focus/linear focused design to suit the different needs of diverse applications.

Leveraging bialkali photocathode with high blue sensitivity and luminous sensitivity, our standard PMT tube detector covers the wavelength range of 290-650nm, with a quantum efficiency (QE) peak wavelength at 380nm, the spectral response matching well with the blue light and visible light emission spectra of scintillators. 

Our SPMT-F021 photomultiplier tube series features high gain and high collection efficiencies, these photomultiplier tubes supplied by Shalom EO have active cathode areas of dia 46mm at minimum and 15 pin base, while harnessing a box-and-grid design structure for the dynodes and the anode, where the dynodes are arranged in a sequence inside a defined housing, and grid structure is employed for dynode that guides the electrons to ensure electrons follow a defined path, reducing the chance of electron loss or scattering and improves the efficiencies for the eventual collection of photoelectrons. Utilizing multiple dynode stages, when the applied voltage potential is sufficient as specified, the gains of Shalom EO’s standard photomultipliers can reach several times ten million. The SPMT-F021 photomultiplier tubes are premium for applications like scintillation counter and in the realm of high energy physics.

Our SPMT-T013 standard photomultiplier series boasts fast response and low noise with a typical rise time of 1.9ns and a typical dark current value of 2nA. The SPMT-T013 photomultiplier tubes integrate a 14-pin base and use a box-focused or linear-focused dynode structure, where the box-focused design is more suitable for high-precision applications and the PMTs with linear-focused structure is a cheaper option for general purpose application. The SPMT-T013 standard photomultipliers are excellent for applications like scintillation counter and radiation measuring.

General Specifications:

Figure1.SPMT-F021-Typical Gain Curve

Figure2.SPMT-F021-Typical Spectral Reponse

Figure3.SPMT-T013-Typical Gain Curve

Figure4.SPMT-T013-Typical Spectral Reponse

Figure5.SPMT-F021-Dimensional Outline

Figure6.SPMT-F021-Voltage Distribution Diagram

Figure7.SPMT-T013-Dimensional Outline

Figure8.SPMT-T013-Voltage Distribution Diagram