  Through resonant backward Raman scattering, the plasma wave mediates the
energy transfer between long pump and short seed laser pulses. These mediation
can result in pulse compression at extraordinarily high powers. However, both
the overall efficiency of the energy transfer and the duration of the amplified
pulse depend upon the persistence of the plasma wave excitation. At least with
respect to the recent state-of-the-art experiments, it is possible to deduce
that at present the experimentally realized efficiency of the amplifier is
likely constrained mainly by two effects, namely the pump chirp and the plasma
wave wavebreaking.
