Aleshire, ChristopherChristopherAleshireSteinkopff, AlbrechtAlbrechtSteinkopffKarst, MaximilianMaximilianKarstKlenke, ArnoArnoKlenkeJauregui, CesarCesarJaureguiKuhn, StefanStefanKuhnNold, JohannesJohannesNoldHaarlammert, NicolettaNicolettaHaarlammertSchreiber, ThomasThomasSchreiberLimpert, JensJensLimpert2022-09-202022-09-202022https://publica.fraunhofer.de/handle/publica/42586510.1117/12.26095692-s2.0-85131220431In-house fabricated Ytterbium-doped rod-type multicore fibers (MCFs) with 4x4 cores were used to generate and amplify ns-class pulses to energies up to 37 mJ. Amplification was compared using tapered and untapered MCFs with large multimode output cores using a Q-switched MCF oscillator as seed source. The tapered fiber improves beam quality (average M2 = 1.56) while maintaining a large waveguide mode area for suppression of nonlinear effects and increased amplification per unit length. These all-glass MCFs can facilitate energy and power scaling in compact high power coherently combined amplifier systems.enFiber lasersHigh power lasersMulticore fibersOptical fibersconference paper