About PMTs | Photomultiplier tubes (PMTs)

What is a photomultiplier tube (PMT)?

A photomultiplier tube (PMT) is a highly sensitive vacuum device designed to detect and amplify extremely low levels of light, down to a single photon.

It operates by converting incoming photons into electrons via the photoelectric effect, then multiplying those electrons through a series of dynodes to generate a measurable electrical signal.

PMTs are valued for their exceptional sensitivity, fast response times, and low noise. They are widely used in applications such as medical imaging, nuclear and particle physics, spectroscopy, and industrial inspection where precise and reliable detection of faint light signals is essential.

Behind high-performance PMTs

Hamamatsu’s precision glass fabrication, from complex shaping to electrode assembly, is fundamental to reliable photomultiplier tube performance. Our in-house manufacturing expertise and craftsmanship support PMTs and related components used across scientific and industrial detection applications.

Building on decades of vacuum tube technology, Hamamatsu develops and manufactures PMTs through fully integrated, proprietary processes. These include glass processing, electrode assembly, sealing, evacuation, and rigorous inspection, all contributing to high performance and long-term reliability.

Our capabilities enable a broad range of PMTs with different shapes, sizes, and spectral sensitivities. Combined with specialized in-house expertise and skilled craftsmanship, we support both high-mix, low-volume production and flexible product development tailored to diverse customer requirements.

Vacuum technology

Photomultiplier tubes convert light into electrical signals using the external photoelectric effect. Electrons emitted from the photocathode are guided by focusing electrodes, multiplied through dynodes, and finally collected at the anode as an electrical signal.

This process requires a precisely controlled vacuum environment. The stability and quality of the vacuum directly influence electron motion, signal amplification, and overall device performance.

Vacuum technology is also essential during manufacturing. It plays a critical role in processes such as photocathode deposition and the formation of secondary-emission surfaces, both of which directly impact sensitivity, stability, and reliability.

Multiplication principle

These animations illustrate the electron multiplication process inside a photomultiplier tube from the moment light enters the device to the generation of an amplified electrical signal. They provide a clear, intuitive view, intuitive view of how weak optical signals are converted into measurable outputs.

Side-on type

Head-on type

Main components

A PMT consists of three main components: the light input window, the photocathode, and the electron multiplier (dynodes). Incident light first passes through the light input window and is converted into electrons at the photocathode. Those electrons are then multiplied by the dynodes and finally extracted as an electrical signal.

Light input window

The light input window allows incident light to enter the PMT.

The choice of window material determines the transmittable wavelength range, especially at shorter wavelengths, and therefore influences the usable spectral range and sensitivity of the device.

Typical materials include:

Borosilicate glass
Quartz glass
UV-transmitting glass
MgF₂crystal

Photocathode

The photocathode is a thin photosensitive layer deposited on the inner surface of the light input window. It converts incident photons into electrons. The material composition of the photocathode strongly influences the spectral response and sensitivity of the PMT, making it a key factor in overall device performance.

Typical photocathode types include:

Bialkali
Multialkali
Solar blind (Cs-I and Cs-Te)
Crystalline materials (e.g. GaAsP, GaAs)

Electron multiplier (dynodes)

The electron multiplier consists of a series of electrodes called dynodes. Electrons emitted from the photocathode are multiplied by secondary electron emission at the dynodes, amplifying weak signals to detectable levels. The dynode structure influences gain, timing characteristics, and overall performance.

Typical dynode structures include:

Circular-cage type
Box-and-grid type
Linear-focused type
Metal channel type

Pursuing even higher performance

Hamamatsu Photonics continuously advances photomultiplier tube technology by improving not only sensitivity, but also a wide range of performance characteristics, including timing resolution, stability, and durability.

Through ongoing innovation in materials, design, and manufacturing processes, we strive to enable increasingly precise and reliable light detection, supporting the evolving needs of scientific, medical, and industrial applications.

Example of 20-inch PMTs for academic research:


Facility name	Kamiokande (From 1983 to 1996)	SuperKamiokande (From 1996 to present)	HyperKamiokande (In planning stage)
Type No.	R1449	R3600	R12860
Electron transit time spread	8.0 ns	5.5 ns	2.4 ns

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About PMTs | Photomultiplier tubes (PMTs)

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