  Optical quadratic nonlinearity is ultrafast in nature, while parametric
interaction usually manifests only the broadband characteristic. Enormous
progress has been made toward broadband phase-matching for parametric
amplification and wide applications. In existing devices of broadband
parametric amplification, the power efficiency of conversion is restricted to
approximately the energy efficiency, and the desire for the signal power
enhancement necessitates additional pulse compression after amplification.
Here, we demonstrate ultrafast parametric amplification having an extraordinary
power efficiency of 1155%; this allows the generation of intense femtosecond
pulses without the need for a pulse stretcher and compressor. Direct
femtosecond signal amplification by picosecond pumping is enabled by an
ultrafast parametric environment in which the pre-delayed signal of faster
speed gradually overtakes and effectively depletes the pump of slower speed as
they propagate in a nonlinear crystal. The demonstrated technique should lead
to breakthroughs in ultrafast lasers as well as applications.
