  Femtosecond optical pump-probe technique is used to study charge carrier
dynamics in few-layer MoS2 samples fabricated by mechanical exfoliation. An
ultrafast pump pulse excites carriers and differential reflection of a probe
pulse tuned to an excitonic resonance is detected. We find that the spectrum of
the differential reflection signal is similar to the derivative of the
resonance. The decay time of the signal is in the range of 150 to 400 ps,
increasing with the probe wavelength. With a fixed probe wavelength, the signal
magnitude is proportional to the pump fluence, while the decay time is
independent of it.
