  Orbital angular momentum (OAM) based structured light beams provide an
additional degree of freedom for practical applications ranging from optical
communication to laser-based material processing. Many techniques exist for
generating such beams within laser sources and these primarily rely upon the
use of specially designed optical components that limit laser power scaling and
ready tunability of the topological charge and polarization of the output OAM
beams. Here we show that some of these limitations can be overcome by employing
a computer controlled reflective phase-only spatial light modulator (SLM) to
adaptively tailor the input (and subsequent output) beam wavefront and
polarization in a few-mode fibre amplifier. In this way modal-coupling induced
beam distortion within the fibre amplifier can be mitigated and we are able to
generate at will any desired supported spatial mode guided in the fibre,
including conventional LP modes, scalar OAM modes and cylindrical vector modes,
at average powers >10 W and with a peak power of >11 kW. Our results pave the
way to the realization of practical high-power structured laser sources with
tunable chirality and polarization.
