Spectroscopy and efficient OPSL-pumped laser operation of Er:BaF₂ crystal at 2.8 µm

We present growth, spectroscopy and efficient laser operation of the cubic fluoride crystal Er:BaF₂ at 2.8 µm. An Er(3.6 at.%):BaF₂ crystal was grown by the vertical Bridgman method. We reveal the thermal conductivities of pure BaF₂ and Er:BaF₂ crystals for different temperatures. The temperature-dependent cryogenic absorption spectra were investigated in the near-infrared range, and we determined the energetic positions of the Stark levels of the upper and lower laser multiplets ⁴I_11/2 and ⁴I_13/2, respectively. A strong absorption peak at 971.5 nm and a broad gain bandwidth around 2.7-2.9 µm with a large emission cross section at 2732 nm were found. Under pumping with an optically-pumped semiconductor laser (OPSL) at 971.5 nm, we obtained 0.4 W of output power at a wavelength of 2786 nm with a slope efficiency of 31%. The slope efficiency is the highest in reported for 3 µm lasers based on Er:BaF₂ at present.