Optimizing rod-type multicore fiber amplifiers in coherently-combined laser systems

Coherent beam combination of fiber amplifiers is a powerful tool to synthetically increase the effective mode area of the beam while mitigating most of the limitations of fibers. Therefore this technique enables a further power and energy scaling of the radiation emitted by fiber laser systems (even of those delivering ultrafast pulses) [1] , [2] . However, the combination of single emitters leads to very complex, bulky and expensive systems due to the component count growing linearly with the number of channels. To decouple the component count from the channel count, so called multicore fibers (MCFs), that incorporate multiple active cores sharing the same pump cladding, have been developed. First tests with MCF amplifiers have not only shown their linear power scaling potential but also the scaling of the transverse mode instability threshold [3] .