PhotomultiplierVorverstärkung

Photomultiplier tube (PMT) is a highly sensitive vacuum electronic device that converts light into an electrical signal with high gain. It consists of a sealed glass envelope containing a photocathode, a series of dynodes, and an anode. Incidence of photons causes emission of photoelectrons at the photocathode via the photoelectric effect. These electrons are accelerated toward the first dynode by a high voltage; each dynode stage multiplies the number of electrons, producing gains of typically 10^6 to 10^8. The final electron current is collected at the anode, yielding pulses proportional to the light intensity.

Materials and variants: Photocathode choices determine spectral response (for example bialkali for visible, Cs-Te for the UV). Dynode chain design (linear or cross-focused) affects gain and timing. Some PMTs use microchannel plates for higher timing resolution and compact form factors.

Performance: PMTs are capable of single-photon detection, fast timing (rise times of a few nanoseconds), and low noise when shielded from light. Limitations include the need for high voltage (typically a few hundred to a thousand volts), sensitivity to magnetic fields, vulnerability to damage by bright light, and relatively large size and fragility. They also have dark current and afterpulsing.

Applications: Widely used in experimental physics (particle detectors, Cherenkov counters, scintillation counters), astronomy and night-sky imaging, medical imaging (PET and SPECT), and various scientific instrumentation.

History: The first practical PMTs were developed in the 1930s and quickly adopted by physics and industry; over decades versions such as dynode PMTs, microchannel plate PMTs, and hybrid photodetectors expanded capabilities.