Red upconversion Yb-sensitised Pr fluoride fibre laser pumped in 0.8 mu m region

Room temperature upconversion lasing has been obtained at 635 nm in Yb:Pr codoped fluoride fibre pumped in the 0.8 mu m region. YB³⁺ is excited by ground state absorption and transfers energy to the ¹G₄ level of Pr³⁺, which is then brought into the ³P₀ level by excited state absorption. Extracted powers in excess of 20 mW at 635 nm and a slope efficiency of 10% were observed for 840-850 nm.