photoncount

Photoncount, often rendered as photon counting, refers to the measurement and recording of individual photon detection events. It is a technique used across optics and photonics to quantify very low light levels by registering discrete photon arrivals rather than integrating continuous optical power. Photoncount methods exploit detectors capable of single-photon sensitivity and fast temporal resolution.

Common detectors used in photoncount systems include photomultiplier tubes, single-photon avalanche diodes, superconducting nanowire single-photon detectors, and transition-edge sensors. Measurement modes range from simple counting of events (counts per second) to time-correlated single-photon counting, which records arrival times to build timing histograms for lifetime and correlation studies. Photoncount data typically follow Poisson statistics at low flux and require calibration for quantum efficiency, dark counts, dead time, and afterpulsing.

Applications of photoncount techniques span astronomy, fluorescence and single-molecule microscopy, lidar and ranging, optical communication, and quantum optics experiments such as quantum key distribution and photon correlation measurements. Advantages include high sensitivity and the ability to resolve temporal photon statistics; limitations involve detector nonidealities, limited dynamic range, and the need for careful signal processing to distinguish true photon events from noise. Photoncount remains a fundamental approach where detecting and characterizing individual quanta of light is necessary.