  We present measurements on pulsed four-wave mixing involving a Rydberg state
in an atomic vapor cell. The excitation to the Rydberg state is conducted by a
pulsed two-photon excitation on the nanosecond timescale that is combined with
a third CW laser in phase-matched geometry yielding light emission on the same
timescale. An additional signal peak is observed shortly after the pulse that
can be attributed to a revival of constructive interference between different
velocity classes of the radiating atomic dipoles. Furthermore we investigate
the density dependence of the four-wave mixing signal. From the shape of the
respective curve we are able to confirm energy and momentum conservation in the
photonic part of the system.
