Abstract
The mid-infrared (MIR) emission behavior of Tb3+-doped Ge–As–Ga–Se bulk glasses (500, 1000, and 1500 ppmw Tb3+) and unstructured fiber (500 ppmw Tb3+) is investigated when pumping at 2.013 μm. A broad emission band is observed at 4.3–6.0 μm corresponding to F57→F67, with an observed emission lifetime of 12.9 ms at 4.7 μm. The F47 level is depopulated nonradiatively and so it is proposed that Tb3+-doped Ge–As–Ga–Se fiber may operate as a quasi-three-level MIR fiber laser. Underlying glass-impurity vibrational absorption bands are numerically removed to give the true Tb3+ absorption cross section, as required for Judd–Ofelt (J–O) analysis. Radiative transition rates calculated from J–O theory are compared with measured lifetimes. A numerical model of the three-level Tb3+-doped fiber laser is developed for Tb3+ doping of 8.25×1024 ions m−3 (i.e., 500 ppmw) and dependence of laser performance on fiber length, output coupler reflectivity, pump wavelength, signal wavelength, and fiber background loss is calculated. Results indicate the feasibility of an efficient three-level MIR fiber laser operating within 4.5–5.3 μm, pumped at either 2.013 or 2.95 μm.
Highlights
Selenide-chalcogenide glasses have a phonon energy of ∼300 cm−1, a theoretical low optical-loss window of ∼100 dBkm−1 across ∼3–10 μm in the mid-infrared (MIR) spectral region, and large refractive indices (∼2.5–2.8)
Rare earth (RE) ions doped in a selenide glass host exhibit long radiative lifetimes and large absorption and emission cross sections [1]
One problem is the long lifetimes of adjacent rare earth (RE) electronic levels, in a selenide glass host, which tend to self-terminate, precluding lasing [4]
Summary
Selenide-chalcogenide glasses have a phonon energy of ∼300 cm−1, a theoretical low optical-loss window of ∼100 dBkm−1 across ∼3–10 μm in the mid-infrared (MIR) spectral region, and large refractive indices (∼2.5–2.8). Rare earth (RE) ions doped in a selenide glass host exhibit long radiative lifetimes and large absorption and emission cross sections [1]. One problem is the long lifetimes of adjacent RE electronic levels, in a selenide glass host, which tend to self-terminate, precluding lasing [4]. We show that in Tb3-doped Ge–As–Ga–Se glasses, when pumping into the 7F4 level, the emission transitions from 7F4, 7F3, 7F2, 7F1, or 7F0 levels are expected to be quenched and quickly relax to the long-lived 7F5 manifold; quasi-MIR three-level laser action is possible for the 7F5 → 7F6 transition, i.e., from the first excited state to the ground state
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