New room temperature CW laser at 2.82 μm: U3+/LiYF 4

Recently, optical studies of U doped LiYF₄(YLF) have been made. The authors show that U/YLF is a promising IR laser because the crystal field Stark level splitting of the ₄I_9/2 ground multiplet (1113cm^-1) is larger than in U³⁺ /CaF (609cm^-1) which makes a four level laser possible at room temperature. However the valence state 3+ is not the most stable state for the actinide ion and the absorption spectra, as well as the pale green colour, show that usually both valence states U³⁺ and U⁴⁺ are present in the crystal. This Letter reports the first observation of CW laser emission of U³⁺ in LiYF₄ at room temperature at 2.82 μm