Multi-Watt Multi-Pass Amplification in a 42-mm-Long Yb:LuLiF4 Single Crystal Fiber Grown by the Micro-Pulling-Down Method

By exploiting a more favourable surface/volume ratio for heat exchange and pump absorption distribution over significantly increased length, single crystal fibers (SCF) are considered promising candidate as a replacement for bulk crystals in high-power laser systems. So far, micro-pulling down (μ-PD) technique was successfully employed mainly in growing cubic crystals, most impressive results being obtained with Yb:YAG [1]. Birefringent sCf are also attractive, as they provide a quite straightforward means of avoiding beam quality degradation at high thermal load due to depolarization. The first Nd:YLF laser based on fiber crystals was reported in [2]. However, from the perspective of high-power applications, Ytterbium-doped materials are definitely more interesting, owing to the much smaller quantum defect and absence of excited-state absorption.