Fibre Lasers for Particle Accelerators

Laser driven plasma wakefield accelerators (LWFA) are one possible
candidate for the next generation of particle accelerators. They are capable of
producing accelerating gradients several orders of magnitude higher than those of
conventional RF accelerators. Despite the significant promise of this technology,
there is still work needed in several areas in order to build a functional LWFA and
one such area is the laser used to drive the wakefield. Current laser technology
allows us to obtain high repetition rates, high average and high peak powers, but
not all at the same time, one generally loses out in at least one area whilst making
gains in another. To drive a wakefield within a plasma a high peak power is required
and whilst this is achievable with current technology, the repetition rate of these
lasers are very low and thus would not allow them to compete with conventional RF
accelerators.
Fibre lasers are capable of delivering high repetition rates, high average power and
high wall-plug efficiency and for these reasons they have been highlighted as a
candidate for driving a plasma wakefield accelerator. In particular, the high
repetition rates achieved by fibre lasers coupled with the high average power mean
that if a high enough peak power could be achieved, this could be a suitable set up
for a functional LWFA. This thesis will focus on the coherent combination of fibre
lasers to achieve high peak power whilst maintaining high average power, high
repetition rates and high wall-plug efficiency.
Coherent combination of fibre lasers has been demonstrated experimentally for
arrays of 10s of fibres but to build a LWFA with energies close to that of modern
RF accelerators it may be necessary to combine 1000s of fibre lasers. In particular
this thesis will focus on how to increase and maintain combining efficiency when
building up a large array of fibre lasers.