Single photon counting detectors in action: Retrospect and prospect

Single photon counting (SPC) techniques, which were devised and developed over decades relying on Photomultiplier tubes (PMT), gained new impulse from silicon single-photon avalanche diodes (SPADs). The relative merits of PMTs and SPADs as workhorses for experimenters are assessed and prospects of new SPAD developments are outlined. Trends and prospects of development of integrated SPAD arrays are also discussed.