We investigate the hot carrier dynamics further by two-pulse coincidence (2PC) measurements in vacuum using ASOPS. Briefly, the device is excited by the two pulsed lasers A and B (pump and probe) separated by a delay time Δt. The corresponding photoresponse collected by the lock-in amplifier is recorded as a function of delay time Δt between the pulses (Figure ) and hence the technique is also called photocurrent autocorrelation . In a typical 2PC measurements, when the pump and the probe lasers coincide spatially and temporally, the generation of photocurrent by the probe is suppressed because of the saturation in the ground state, causing a prominent dip at the zero time delay Δt = 0. With an increase in the delay time, parts of the pump-induced charge carriers relax, and they can be excited again by the probe beam. Hence, one would expect an exponential recovery of photocurrent with the delay time Δt. Our WS2/graphene heterostructure device exhibits two lifetime components (Figure ) with τfast = 3 ps (Figure ) and τslow  500 ps (Supporting In formation Section 3), indicating the presence of two distinct dynamic processes. The fast component appears as a peak (positive contribution to the photocurrent) and the slow component as a dip (negative contribution).