Continuous-wave and Fe2+:ZnSe passively Q-switched mid-infrared lasers based on 2at.% Er3+:CaF2 crystal

A compact high-power 2.8-µm laser with a 2 at.%-doped Er³⁺:CaF₂ crystal was demonstrated, which delivered a maximum output power of 2.848 W with a slope efficiency of 26.3 %. To the best of our knowledge, this is the highest output power among all the reported LD end-pumped Er³⁺-doped fluoride crystal lasers. Experimentally, the negative thermal lens effect was characterized and the thermal lens optical diopters for two axes were obtained as M_x = -0.21 m⁻¹/W and M_y = -0.33 m⁻¹/W. In addition, the visible fluorescence spectra of Er³⁺:CaF₂ crystal with and without laser operation were measured and analyzed. With Fe²⁺:ZnSe as saturable absorber, a passively Q-switched 2.759-µm Er³⁺:CaF₂ laser with an average output power of 75 mW, a peak power of 2.39 W, a single pulse energy of 1.81 µJ, and a pulse width of 755.3 ns was obtained at a repetition rate of 41.55 kHz.