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Two different mid-infrared (mid-IR) crystalline laser active media of Zn1-xMnxSe and Zn1-xMgxSe with similar manganese or magnesium ions amount of x ≈ 0.3 co-doped by divalent chromium (Cr2+) and iron (Fe2+) ions were investigated at cryogenic temperatures and compared for different excitation wavelengths used. Both single crystals were synthesized by high pressure Bridgman method and their thickness were 2.6 mm and 5 mm, respectively. Crystals were investigated under three excitation wavelengths of the Q-switched Er3+:YLF laser at ~1.73 μm, Q-switched Er3+:YAG laser at ~2.94 μm, and the gain-switched Fe2+:ZnSe laser operated at liquid nitrogen temperature of 78 K at a wavelength of ~4.05 μm. Spectroscopic and laser output characteristics were measured: absorption and fluorescence spectra, laser output pulse duration, mean output energy, and laser oscillation spectra. Both laser systems were able to generate radiation by Cr2+ or by Fe2+ ions under direct excitation, or by Fe2+ ions via the Cr2+ → Fe2+ energy transfer depending on the excitation wavelength and the output coupler conditions. Fe2+ ions in Cr2+,Fe2+:Zn1-xMnxSe and Cr2+,Fe2+:Zn1-xMgxSe (x ≈ 0.3) laser systems at 78 K pumped by Er3+:YLF laser radiation at ~1.73 μm via the energy transfer mechanism generated laser radiation at the wavelengths of ~4.4 μm and ~4.8 μm at 78 K, respectively. Obtained results have shown a possibility of developing novel coherent laser systems in mid-IR region (~2.3 – 2.5 μm and ~4.4 – 4.9 μm) based on AIIBVI matrices. Thus, possibility to excite the Fe2+ active ions in both samples directly by ~2.94 μm as well as ~4.05 μm radiation or eventually in a compact way through the Cr2+ → Fe2+ ions energy transfer-based mechanism by ~1.73 μm radiation was demonstrated.
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