  We propose and demonstrate a method to characterize a gated InGaAs
single-photon detector (SPD). Ultrashort weak coherent pulses, from a
mode-locked sub-picosecond pulsed laser, were used to measure photon counts, at
varying arrival times relative to the start of the SPD gate voltage. The uneven
detection probabilities within the gate window were used to estimate the
afterpulse probability with respect to various detector parameters: excess
bias, width of gate window and hold-off time. We estimated a lifetime of 2.1
microseconds for the half-life of trapped carriers, using a power-law fit to
the decay in afterpulse probability. Finally, we quantify the timing jitter of
the SPD using a time to digital converter with a resolution of 55 ps.
