Dead-time effect on SPAD detection efficiency.

Single-photon detectors that operate in the Geiger-mode provide a large potential for low-light detection. However, the detection rate is affected and limited by the inherent dead-time of the detector. This work compares simulation with experimental results to demonstrate the dependence of the effective efficiency of the single-photon avalanche-diode detector on the length of the dead-time. Analytical expressions are derived to understand the dependence, which is different for a free-running detector and one operating in a gated mode of detection. The results, from simulation and experiment, demonstrate the sensitivity to the detector dead-time, and the difference between both operational modes. In general, the gated mode is superior, and at particular conditions, the efficiency can actually improve with extended dead-times. However, for long dead-times at significant background conditions, the free-running mode can compete with the gated mode in terms of efficiency, while also being independent of the timing of the signal within the measurement.