Progress in rare-earth-doped mid-infrared fiber lasers

TLDR

The review discusses progress and challenges in fabricating rare‑earth‑doped chalcogenide‑glass fibers for mid‑infrared fiber lasers. The study proposes a coherent explanation for the failure of gallium‑lanthanum‑sulfide glass mid‑IR fiber lasers, introduces impurity‑multiphonon relaxation as a new non‑radiative depopulation mechanism, and outlines potential applications of mid‑IR fiber lasers. The authors emphasize optimizing covalent chalcogenide glass hosts and processing routes to reduce non‑radiative decay, avoid rare‑earth clustering, and prevent devitrification. They present practical characterization results of candidate selenide glasses.

Abstract

The progress, and current challenges, in fabricating rare-earth-doped chalcogenide-glass fibers for developing mid-infrared (IR) fiber lasers are reviewed. For the first time a coherent explanation is forwarded for the failure to date to develop a gallium-lanthanum-sulfide glass mid-IR fiber laser. For the more covalent chalcogenide glasses, the importance of optimizing the glass host and glass processing routes in order to minimize non-radiative decay and to avoid rare earth ion clustering and glass devitrification is discussed. For the first time a new idea is explored to explain an additional method of non-radiative depopulation of the excited state in the mid-IR that has not been properly recognized before: that of impurity multiphonon relaxation. Practical characterization of candidate selenide glasses is presented. Potential applications of mid-infrared fiber lasers are suggested.