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

Abstract

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.

Fig. 1

Circuit diagram of the optical gating scheme.

Fig. 2

(Color online) Experimental setup of the time-gated single-photon counting system. BS, beam splitter; M, mirror; PMT, photomultiplier tube; Amp, amplifier stage; CFD, constant fraction discriminator.

Fig. 3

(Color online) Impulse response of the time-gated single-photon counting system.

Fig. 4

(Color online) TPSF of a 6 cm⁻¹ reduced scattering coefficient intralipid solution compared with the analytical result. The solution is in a transparent container of 3.2 cm thickness.

Fig. 5

(Color online) Setup for detecting and resolving two targets separated by 4 mm embedded in a highly scattering medium.

Fig. 6

(Color online) Normalized photon counts obtained for the target-pair positions across the laser beam path. The target locations with respect to the counts are also indicated.