Aleshire, Christopher E.Christopher E.AleshireEichner, TimoTimoEichnerSteinkopff, AlbrechtAlbrechtSteinkopffKlenke, ArnoArnoKlenkeJauregui, CesarCesarJaureguiPalmer, GuidoGuidoPalmerKuhn, StefanStefanKuhnNold, JohannesJohannesNoldHaarlammert, NicolettaNicolettaHaarlammertLeemans, Wim P.Wim P.LeemansSchreiber, ThomasThomasSchreiberMaier, Andreas R.Andreas R.MaierLimpert, JensJensLimpert2023-10-172023-10-172023https://publica.fraunhofer.de/handle/publica/45181210.1364/OL.4873342-s2.0-8515256215237058676Frequency doubling of a Q-switched Yb-doped rod-type 4 × 4 multicore fiber (MCF) laser system is reported. A second harmonic generation (SHG) efficiency of up to 52% was achieved with type I non-critically phase-matched lithium triborate (LBO), with a total SHG pulse energy of up to 17 mJ obtained at 1 kHz repetition rate. The dense parallel arrangement of amplifying cores into a shared pump cladding enables a significant increase in the energy capacity of active fibers. The frequency-doubled MCF architecture is compatible with high-repetition-rate and high-average-power operation and may provide an efficient alternative to bulk solid-state systems as pump sources for high-energy titanium-doped sapphire lasers.enjournal article