  One of the key properties of single-photon detectors is their recovery time,
i.e. the time required for the detector to recover its nominal efficiency. In
the case of superconducting nanowire single-photon detectors (SNSPDs), which
can feature extremely short recovery times in free-running mode, a precise
characterisation of this recovery time and its time dynamics is essential for
many quantum optics or quantum communication experiments. We introduce a fast
and simple method to characterise precisely the recovery time of SNSPDs. It
provides full information about the recovery of the efficiency in time for a
single or several consecutive detections. We also show how the method can be
used to gain insight into the behaviour of the bias current inside the nanowire
after a detection, which allows predicting the behaviour of the detector and
its efficiency in any practical experiment using these detectors.
