The influence of Cr2+ to Fe2+ ions concentration ratio on the Cr,Fe:Zn(1-x)Mn(x)Se (x ≈ 0.15) laser properties excited via Cr2+ → Fe2+ energy transfer

Abstract

In this work the results of research of an optimal concentration ratio of Cr²⁺ and Fe²⁺ co-doped active ions for more efficient Cr²⁺ → Fe²⁺ ions energy transfer in a chosen Zn_1-xMn_xSe (x ≈ 0.15) host material are presented. Three cryogenically cooled Cr²⁺,Fe²⁺:Zn_1-xMn_xSe (x ≈ 0.15) single crystals with the same thickness of ~2.7 mm and with different doping ratios of Cr²⁺ and Fe²⁺ ions of ~1:1, ~2:1, and ∼3:1 were investigated under Q-switched Er:YLF laser excitation (wavelength: ∼1.73 μm, pulse energy: ∼10 mJ, pulse duration: ∼150 ns). The temperature dependence of the absorption and fluorescence spectra, the fluorescence decay time as well as the laser output characteristics were measured. The Fe²⁺ ions maximum laser output of ~50 μJ at the wavelength range of ~4.25-4.42 μm was obtained with the crystal sample for which the active ions ratio was ~2:1. A further increase of the chromium ions amount (Cr²⁺:Fe²⁺ ≈ 3:1) led to worse results. Using appropriate resonator cavity mirrors, the samples were also able to generate the ~2.35-2.45 μm laser radiation from Cr²⁺ ions. The laser output beam spatial profiles were close to Gaussian in all cases. In summary, an optimized compact source of mid-infrared ~4.25-4.42 μm (Fe²⁺) and ~2.35-2.45 μm (Cr²⁺) of Cr,Fe:Zn_1-xMn_xSe (x ≈ 0.15) crystal pumped via Cr²⁺ ions by the ~1.73 μm radiation is described.