Single-Photon Detector: Dead Time & Dark Counts

This simulator models a real single-photon avalanche diode (SPAD) as used in quantum key distribution, LIDAR and fluorescence-lifetime imaging. Photons arrive as a Poisson process at a tunable rate and are detected with a tunable quantum efficiency; every avalanche triggers a non-paralyzable dead time during which the diode is blind, and two independent noise mechanisms — thermal dark counts and trap-release afterpulsing — add spurious clicks of their own. A 3D timeline renders every click as it happens, color-coded by cause, with a dead-time shadow trailing each event, while live counters track the true detection rate, the noise floor, the fraction of time the detector is unavailable, and the resulting signal-to-noise ratio.