Lenski, MathiasMathiasLenskiXu, QianQianXuGierschke, PhilippPhilippGierschkeWang, ZiyaoZiyaoWangHeuermann, TobiasTobiasHeuermannJauregui Misas, CesarCesarJauregui MisasLimpert, JensJensLimpert2025-06-132025-06-132025https://publica.fraunhofer.de/handle/publica/48861510.1364/OE.5536402-s2.0-10500226186640219501This contribution explores the average-power scaling potential of in-band pumped, Thulium (Tm-) doped fiber amplifiers for high peak-power operation. These results have been obtained by pumping a Tm-doped, photonic crystal fiber at a wavelength around 1700nm. In one of the experiments reported in this work an average output power of 242 W with a slope efficiency of 80% was obtained. Additionally, we also demonstrate operation up to an average output power of 80 W with no need for active cooling, which further highlights the benefits of this low-quantum defect pump approach. Furthermore, our simulation reveals the average power scaling potential of these systems to the multi-kilowatt level.entruejournal article