Abstract
Rare-earth-doped fluoride fiber provides a compact and robust platform for getting mid-infrared laser at 3∼5 μm that can find direct applications in the fields of spectroscopy, polymer processing, and infrared countermeasures. Based on this strategy, the longest wavelength has been experimentally pushed to ∼3.9 μm, from an 888 nm pumped 10 mol.% heavily-Ho3+-doped InF3 fiber laser [Optica, vol. 5, no. 7, pp. 761--764, 2018]. Its great heat load however, limits the output to ∼200 mW. To solve this problem, we theoretically propose a novel scheme, enabling high-power output with significantly reduced heat load, in which both the concepts of cascaded pumping and transitions have been simultaneously used. Specifically, the dual-wavelength pumping at 1950 nm and 1650 nm (i.e., 5I8→5I7→5I5) is exploited to excite a 1 mol.% lightly-Ho3+- doped InF3 fiber, and the cascaded transitions at ∼3.9 μm and ∼2.9 μm (i.e., 5I5→5I6→5I7) are activated. Consequently, >10 W ∼3.9 μm and >12 W ∼2.9 μm laser outputs have been predicted with the optical-to-optical efficiencies of 31.69% and 40.13%, respectively, indicating at least 50 times power enhancement at ∼3.9 μm. More importantly, the heat load of the pumped fiber end, which is most easily damaged, is only 12.6% of the aforementioned heavily-Ho3+ -doped system. Further power scaling is mainly hampered by the potential optical damage of InF3 glass material. On the whole, our work has offered a promising scheme for significantly improving the performance of Ho3+-doped InF3 fiber laser at ∼3.9 μm, hence paving the way for developing high-power fiber laser technique in this band.
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