  Backward Raman amplification is limited by relativistic nonlinear dephasing
resulting in saturation of the leading spike of the amplified pulse. Pump
detuning is employed to mitigate the relativistic phase mismatch and to
overcome the associated saturation. The amplified pulse can then be reshaped
into a mono-spike pulse with little precursory power ahead of it, with the
maximum intensity increasing by a factor of two. This detuning can be employed
advantageously both in regimes where the group velocity dispersion is
unimportant and where the dispersion is important but small.
