A photon counter can , as its name suggests, the photon counting ! It is used to measure small amounts of light.
Each photon produces a pulse which will last the crossing time of a measuring device (photomultiplier or avalanche photodiode): a pulse height discriminator allows to take into consideration a definite pulses range and not to suffer faults caused by the detector; a pulse shapping is then realized.
Last on the counting line, the photon counter just has to count the number of pulse per second. it is simply consisting in an electronic implementing at each pulse.
In particular HTDS markets one unique and innovative technologie alternative to traditional photomultipliers : the SPCM Module – single photon counter incorporating a photodiode If ODA APD Si.