Comparison of temperature dependence of Fe:ZnSe laser output properties under semi-longitudinal excitation by 2.94 and \(\sim\)4.04 \({\upmu }\)m radiation

The temperature dependence of the laser output properties of the Fe:ZnSe single crystal was compared under its excitation by 2.94 \({\upmu }\)m Q-switched Er:YAG laser radiation and by \(\sim\)4.04 \({\upmu }\)m gain-switched second Fe:ZnSe laser radiation within the same semi-longitudinal configuration. A non-selective laser cavity consisted of a flat highly reflective mirror at \(\sim\)4–5 \({\upmu }\)m and a concave (r = 200 mm) output coupler with a reflectivity of 88% at \(\sim\)3.9\(-\)5.3 \({\upmu }\)m. To keep the energy at both excitation wavelengths the same of \(\sim\)9.4 mJ, a special filters were used for attenuation of 2.94 \({\upmu }\)m radiation. The output energy almost doubled since the angle between pumping and generated laser radiation was reduced from \(\sim\)20\(^{\circ }\) to \(\sim\)12\(^{\circ }\). The generated laser oscillation wavelength was shifted by \(\sim\)100 nm in the case of \(\sim\)4.04 \({\upmu }\)m compared to excitation by 2.94 \({\upmu }\)m radiation. The maximum laser output energy of \(\sim\)1.7 mJ under 2.94 \({\upmu }\)m excitation was obtained at 78 K. However, at \(\sim\)4.04 \({\upmu }\)m pumping, the maximum of \(\sim\)0.5 mJ was obtained at 260 K. The efficiency at 2.94 \({\upmu }\)m excitation decreased from \(\sim\)33% at 78 K to \(\sim\)12% at 340 K. At \(\sim\)4.04 \({\upmu }\)m radiation excitation, the efficiency increased from the laser threshold at 120 K to its maximum of \(\sim\)9% at 260 K.