  Raman and Brillouin amplification of laser pulses in plasma have been shown
to produce picosecond pulses of petawatt power. In previous studies,
filamentation of the probe pulse has been identified as the biggest threat to
the amplification process, especially for Brillouin amplification, which
employs the highest plasma densities. Therefore it has been proposed to perform
Brillouin scattering at densities below $n_{cr}/4$ to reduce the influence of
filamentation. However, parastic Raman scattering can become a problem at such
densities, contrary to densities above $n_{cr}/4$, where it is suppressed. In
this paper, we investigate the influence of parasitic Raman scattering on
Brillouin amplification at densities below $n_{cr}/4$. We expose the specific
problems posed by both Raman backward and forward scattering, and how both
types of scattering can be mitigated, leading to an increased performance of
the Brillouin amplification process.
