Time-gating scheme based on a photodiode for single-photon counting.

A fast, simple, and low-cost optical time-gating scheme for counting single photons is presented. Its construction consists of a silicon photodiode connected in series with a 50 Ω resistor and that operates in the photoconductive mode. The temporal resolution at the FWHM of the photon counting system was measured to be 62 ps. The profile of a single-photon pulse measured with the counting system agreed well with analytical results. The system was also used to successfully resolve a pair of targets with 4 mm separation inside a highly scattering medium by the use of time-gated early-arriving photons.