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.
