SPAd

SPAD is an acronym used in several domains. It is most commonly associated with a French World War I aircraft manufacturer and with a class of photodetectors known as single-photon avalanche diodes.

SPAD (aircraft) refers to the Société Pour l'Aéronautique et ses Développements, a French company formed in the early 1910s that produced advanced fighters during World War I, including the SPAD S.VII and SPAD S.XIII. Under designer Louis Béchereau, SPAD aircraft were known for speed and maneuverability and served with the French Aéronautique Militaire and other Allied air services. After the war, the company ceased independent operations, and its designs influenced postwar French aviation.

SPAD (photodetector) stands for single-photon avalanche diode, a type of semiconductor photodetector operated in Geiger mode. When reverse-biased above the breakdown voltage, a absorbed photon can trigger a self-sustaining avalanche, producing a digital pulse. SPADs offer high sensitivity and excellent timing resolution, making them useful in time-correlated single-photon counting, fluorescence lifetime imaging, LiDAR, and quantum communication. Typical limitations include afterpulsing, dark counts, and dead time, which require careful electronics and cooling in some applications. Arrays of SPADs enable imaging and array-based sensing.

Because SPAD is an acronym used by multiple organizations and technologies, context is required to determine the intended meaning in a given discussion.