Comparison of gain-switched operated Cr2+ and Fe2+ ions co-doped Zn(1-x)Mn(x)Se and Zn(1-x)Mg(x)Se (x ≈ 0.3) lasers in mid-IR under different excitation wavelengths

Abstract

Two different mid-infrared (mid-IR) crystalline laser active media of Zn_1-xMn_xSe and Zn_1-xMg_xSe 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⁺:Zn_1-xMn_xSe and Cr²⁺,Fe²⁺:Zn_1-xMg_xSe (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.