Population of higher-energy levels in LiY_(1-x)Er_xF_4 (x=O.003 ÷1) crystals under CW IR laser-diode pumping

Steady-state population of 7 lowest excited erbium. levels in LiY¬¬_(1-x)Er_xF_4 (YLF:Er^(3+) (x=0.003-1) crystals was studied under upconversion. CW InGaAs laser-diode pumping with varied power density. Theoretical and experimental concentration and power dependencies of population of higher-energy radiative levels were obtained. Relative changes in populations of studied levels in YLF:Er^(3+) crystals were experimentally controlled by visible spectra of steady-state luminescence in the wavelength ranges corresponding to transitions ^4S_(3/2) --> ^4I(15/2) (0.52--0.57) mum and ^4 F_(9/2) --> ^I_(15/2) (0.64--0.68) µm. IR-pumped luminescence kinetic curves of higher-energy transitions ^4S_(3/2) --> ^4I_(15/2) (0.55 µm) and ^2H_(9/2) --> ^4I_(15/2) (0.41 µm) were recorded. The energy-transfer mechanisms were determined, and the predominant mechanisms responsible for upconversion excitation were elucidated. Microparameters of energy transfer and concentration dependencies of the selfquenching rates and non-linear coupling were obtained on the basis of theoretical and experimental estimates of the rates of intra- and intercenter relaxation processes (migration, selfquenching, and upconversion) allowing for statistics of coupling between the impurity centers in the system. The steady-state dependencies of population on the erbium concentration and pumping power density were calculated within the framework of rate balance equations. Good agreement between the theory and experimental data was obtained

Quasi-1D XY Antiferromagnet Sr2Ni(SeO3)2Cl2 at Sakai-Takahashi Phase Diagram

Uniform quasi-one-dimensional integer spin compounds are of interest as a potential realization of the Haldane conjecture of a gapped spin liquid. This phase, however, has to compete with magnetic anisotropy and long-range ordered phases, the implementation of which depends on the ratio of interchain J′ and intrachain J exchange interactions and both uniaxial D and rhombic E single-ion anisotropies. Strontium nickel selenite chloride, Sr2Ni(SeO3)2Cl2, is a spin-1 chain system which passes through a correlations regime at Tmax ~ 12 K to long-range order at TN = 6 K. under external magnetic field it experiences the sequence of spin-flop at Bc1 = 9.0 T and spin-flip transitions Bc2 = 23.7 T prior to full saturation at Bsat = 31.0 T. Density functional theory provides values of the main exchange interactions and uniaxial anisotropy which corroborate the experimental findings. The values of J′/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied sector of the Sakai-Takahashi phase diagram. © 2021, The Author(s).Support by the P220 program of Government of Russia through the project 075-15-2021-604 is acknowledged. ANV acknowledges support by the RFBR Grant 19-02-00015. Work at Heidelberg was supported by BMBF via the project SpinFun (13XP5088) and by Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC2181/1-390900948 (the Heidelberg STRUCTURES Excellence Cluster) and through project KL 1824/13-1. We acknowledge the support of the HLD-HZDR, member of the European Magnetic Field Laboratory (EMFL). Theoretical calculations using density functional theory were supported by the Russian Science Foundation via project 20-62-46047. Experimental research was supported by the Russian Science Foundation via project 19-42-02010

1083 nm ytterbium doped fibre amplifier for optical pumping of helium

International audienceA combination of a narrow linewidth, tunable DBR diode laser and high power ytterbium fibre amplifier in a master oscillator power fibre amplifier (MOPFA) configuration is demonstrated for efficient optical pumping of helium. A compact and efficient diode pumped prototype system is shown to compare favourably with alternative laser sources for production of hyperpolarised He-3 using direct pumping for medical application in MRI