High-efficiency ∼2 μm CW laser operation of LD-pumped Tm3+:CaF2 single-crystal fibers

The Tm:CaF2 single-crystal fibers were successfully grown by modified temperature gradient technique method. The J-O intensity parameters, spontaneous radiative transition rates, radiative lifetimes and fluorescence branching ratios of Tm3+ were calculated with Judd-Ofelt theory. A systematic study of the fluorescence characteristics has been carried out. Simulated emission cross-sections of the F-3(4) -> H-3(6) transition were calculated to be 6.68x10(-21) cm(-2) and 4.65x10(-21) cm(-2) for crystal doped with 3 at.% and 4 at.% Tm3+. The 64.4% slope efficiency with output power of 2.23W was achieved in 3 at.% Tm:CaF2 single-crystal fiber. The slope efficiency decreased to 44.5% and maximum output power decreased to 1.65W in 4 at.% Tm:CaF2 single-crystal fiber. Obtained results show that Tm-doped CaF2 single-crystal fibers are promising materials for IR laser action generation. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement