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8Lasers for mid IR range on the base of rare earth ions doped
chalcogenide glasses
V.V. Koltashev'*, V.G. Plotnichenko1, B.I. Denker2, B.I. Galagan2, S.E. Sverchkov2, M.V. Sukhanov3, A.P. Velmuzhov3, M.P. Frolov4
1-Prokhorov General Physics Institute of the RAS, Dianov Fiber Optics Research Center, Moscow, Russia 2- Prokhorov General Physics Institute of the RAS, Moscow, Russia 3- Devyatykh Institute of Chemistry ofHighPurity Substances of the RAS, Nizhny Novgorod, Russia 4- Lebedev Physical Institute of the RAS Moscow, Russia
Chalcogenide glasses with rare earth doping have long been considered as promising laser materials for mid-infrared spectral range. But only recently bulk and fiber lasers with practically significant efficiency became reality: laser action covering the spectral range of 4.6-6.1 ^m was demonstrated in selenide glasses activated by a number of rare earth ions: Ce3+, Pr3+, Nd3+ and Tb3+ (Fig. 1) [1].
Fig. 1. Rare earth ions energy level schemes Fig. 2. Output power of Tb3+ fiber laser versus incident pump
in selenide laser glasses. power. In the inset: output spectrum.
The directions of our efforts were to maximise the power and efficiency of chalcogenide glass lasers as well as to widen their possible tuning range. To achieve these goals, the unique features of definite laser active ions were successfully used. Tb3+ ions are attractive due to pumping convenience (by ~ 2 ^m Tm3+ or ~ 3 ^m Er3+ pump lasers). Ce3+ ions have the advantage of maximum gain cross section. Nd3+ ions exhibit long-wavelength emission reaching 6 ^m combined with high enough quantum yield. However, the traditionally used optical pumping of neodymium ions at wavelengths of 0.8 or 0.9 microns is not applicable for selenide glasses, since it does not fall into the transparency region of these glasses. Therefore, we proposed an alternative pumping method - a sensitization scheme using Tb3+ ions. In coactivated Tb and Nd glass, Tb3+ ions can absorb radiation from ~2.9 microns ofYAG:Er3+ pump lasers followed by nonradiative transmission to neodymium ions. The results of the laser experiments are summarised in [1].
For Tb3+-doped optical fibers (doping level 1*1019 cm-3) the laser output power up to 200 mW was obtained under 1.908 ^m pumping, slope efficiency was 6.4% (Fig. 2).
For Ce3+-doped optical fibers (doping level 5.5*1018 cm-3) the output power up to 7 mW was obtained under 4.14 ^m pumping, the lasing threshold was as low as 10 mW and the slope efficiency reached 17%.
The tuning range of Nd3+-doped selenide glass laser complements the lasing wavelengths of Ce3+ and Tb3+ lasers (4.5-5.6 ^m) and extends from 5.56 to 6.01 ^m. This wavelength band includes the longest emission wavelengths of any rare-earth doped glass lasers obtained so far.
[1] B. Denker, P. Fjodorow, M. Frolov, B. Galagan, V. Koltashev, V. Plotnichenko, M. Sukhanov, S. Sverchkov, A. Velmuzhov, Rare-Earth-
Doped Selenide Glasses as Laser Materials for the 5-6 ^m Spectral Range, Photonics, vol. 10, 1323 (2023).
