Numerical design of an efficient Ho3+-doped InF3 fiber laser at ∼3.2 ​μm

In this work, we theoretically unlock the potential of Ho3+-doped InF3 fiber for efficient ∼3.2 ​μm laser generation (from the 5F4,5S2→5F5 transition), by employing a novel dual-wavelength pumping scheme at 1150 ​nm and 980 ​nm, for the first time. Under clad-coupled 1150 ​nm pumping of 5 ​W, ∼3.2 ​μm power of 3.6 ​W has been predicted with the optical-to-optical efficiency of 14.4%. Further efficient power scaling, however, is blocked by the output saturation with 980 ​nm pumping. To alleviate this behavior, the cascaded 5I5→5I6 transition, targeting ∼3.9 ​μm, has been activated simultaneously, therefore accelerating the population circulation between the laser upper level 5F4,5S2 and long-lived 5I6 level under 980 ​nm pumping. As a result, enhanced ∼3.2 ​μm power of 4.68 ​W has been obtained with optical-to-optical efficiency of 15.6%. Meanwhile the ∼3.9 ​μm laser, yielding power of 2.76 ​W with optical-to-optical efficiency of 9.2%, is theoretically achievable as well with a moderate heat load, of which the performance is even better than the prior experimentally and theoretically reported Ho3+-doped InF3 fiber lasers emitting at ∼3.9 ​μm alone. This work demonstrates a versatile platform for laser generation at ∼3.2 ​μm and ∼3.9 ​μm, thus providing the new opportunities for many potential applications, e.g., polymer processing, infrared countermeasures, and free-space communications. © 2024 The Authors