Detectors 192
Detectors 192 : Particle Detectors: (4.25) Single-Photon Avalanche Diode: (1) Operating Principle: (1. 4) Saturation: While the avalanche recovery circuit is quenching the avalanche and restoring bias, the SPAD cannot detect photons. Any photons that reach the detector during this brief period are not counted. As the number of photons increases such that the (statistical) time interval between photons gets within a factor of ten or so of the avalanche recovery time, missing counts become statistically significant and the count rate begins to depart from a linear relationship with detected light level. At this point the SPAD begins to saturate. If the light level were to increase further, ultimately to the point where the SPAD immediately avalanches the moment the avalanche recovery circuit restores bias, the count rate reaches a maximum defined purely by the avalanche recovery time (ten million counts per second or more). This can be harmful to the SPAD as it will be experiencing avalanche current nearly continuously
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