  Jitter is one of the key parameters for a superconducting nanowire single
photon detector (SNSPD). Using an optimized time-correlated single photon
counting system for jitter measurement, we extensively studied the dependence
of system jitter on the bias current and working temperature. The
signal-to-noise ratio of the single-photon-response pulse was proven to be an
important factor in system jitter. The final system jitter was reduced to 18 ps
by using a high-critical-current SNSPD, which showed an intrinsic SNSPD jitter
of 15 ps. A laser ranging experiment using a 15-ps SNSPD achieved a record
depth resolution of 3 mm at a wavelength of 1550 nm.
