Performance and wavelength tuning of green emitting terbium lasers

Wavelength tuning experiments in the green spectral range applying Tb³⁺-doped LiLuF₄ and Tb³⁺/Na⁺-codoped CaF₂ single crystals are presented. While in the former case almost 100 mW could be obtained throughout a total range of 7 nm, the inhomogeneously broadened emission features of Tb³⁺ in the CaF₂-matrix allowed for a continuous tuning range exceeding 10 nm. For initial characterization, free running continuous wave laser experiments using Tb³⁺-doped LiLuF₄, Na⁺:CaF₂, and stoichiometric TbF₃ crystals were carried out resulting in efficient continuous wave laser operation in the green spectral region. The density of active centers in TbF₃ is among the highest that can be obtained in solid state gain materials. Nevertheless, a slope efficiency as high as 32% was obtained from this crystal. High Tb³⁺-densities are essential to compensate for the adherent low absorption cross sections at useful pump-wavelengths.