  It is shown theoretically that the use of accelerating spatiotemporal
quasi-phase-matching (QPM) modulation patterns in media with parametric optical
interactions makes it possible to generate a time-reversed replica of the pump
pulse envelope in a frequency converted signal. The conversion is dependent on
the group-velocity mismatch between the fundamental and up-converted harmonics,
and controlled by the acceleration rate (chirp) of the QPM phase pattern.
Analytical results are corroborated by numerical simulations.
