electronmultiplying

Electron multiplying is a process by which a single incoming electron or photon triggers a cascade of secondary electrons, producing a large amplified electric signal. It is a principal gain mechanism in certain vacuum-tube devices and in some solid-state detectors.

A common realization uses a chain of dynodes inside a photomultiplier tube or image intensifier. An incident electron strikes a dynode and liberates several secondary electrons. These electrons are accelerated toward the next dynode, where the process repeats. After N stages, a single initial electron can yield gains on the order of 10^6 to 10^8. This mechanism provides very high sensitivity and fast response, but requires high operating voltage and can be accompanied by gain fluctuations and aging of the dynodes.

Solid-state implementations rely on avalanche multiplication. In reverse-biased avalanche photodiodes or devices designed for Geiger-mode operation, charge carriers gain energy and ionize the lattice, creating additional carriers and an avalanche. Typical gains range from about 10^2 to 10^4 or higher, with operation conditions shaping noise, timing, and stability. While different in details from dynode-based systems, solid-state multipliers achieve comparable signal amplification and are often more compact.

Applications include photon counting and low-light imaging in astronomy and fluorescence spectroscopy, radiation detection, nuclear physics, and medical imaging. Advantages are high gain, fast timing, and single-photon sensitivity. Limitations include the need for high voltage, gain fluctuations and excess noise, aging of components in vacuum devices, dark counts, and afterpulsing; solid-state variants may face breakdown risk and thermal noise.