Xuejian Zhang

Spectral properties of Tm,Ho:LiYF4 laser crystal

Abstract The LiYF 4 single crystal codoped with thulium and holmium ions was successfully grown by the Cz method. The optimal technical parameters obtained were as follows: the pulling rate was 0.16 mm/h; the rotation speed was 3 rpm; the cooling rate was 15 °C/h. The result of XRD curve showed that as-grown Tm,Ho:LiYF 4 laser crystal belonged to the monoclinic system with scheelite-type structure and space group I41/a. The cell parameters calculated were: a =0.52160 nm, c =1.09841 nm and Z =4. Absorption and fluorescence spectra of Tm,Ho:LiYF 4 laser crystal at room temperature were measured and analysed. The absorption cross section, FWHM and absorption coefficient at 779.3 nm calculated were 7.44×10 −21 cm 2 , 8.7 nm and 2.23 cm −1 , respectively. An intensive fluorescence emission peak appeared near 2045 nm. The emission cross section and fluorescence lifetime were 0.87×10 −20 cm 2 and 10.8 ms, respectively. The ratio of Tm-Ho transfer to its back-transfer process was 10.6.

Nanostructured Yb:GGG polycrystalline powders via gel combustion method

Abstract Gadolinium gallium garnet (GGG) nanopowders doped with ytterbium ions (Yb:GGG) were synthesized with citric acid as a fuel via gel combustion method. The optimized conditions for preparing Yb 3+ :Gd 3 Ga 5 O 12 nanopowders were discussed. The heat behavior, structure and morphology of powders were analyzed with thermal analysis (TG-DTA), X-ray diffraction (XRD), infrared spectra (IR) and transmission electron microscope (TEM). TG-DTA analysis revealed that the weight loss of the precursor occured below 800 °C and its crystallization temperature was 830.6 °C. XRD and IR analysis showed that the precursor converted directly into pure GGG at a relatively lower temperature (900 °C) without any other intermediate phase. The lattice constant was 1.2377 calculated by extrapolation method. TEM results indicated that the spherical powders showed good dispersity and had a relatively narrow size distribution with average particle size of approximately 40–50 nm, which was favorable for good sinterability of Yb:GGG laser ceramic.

Growth, structure and spectral characteristics of KEr0.1Yb0.9(WO4)2 laser crystal

Abstract The 10 at.% Er 3+ -doped KYb(WO 4 ) 2 (KEr 0.1 Yb 0.9 (WO 4 ) 2 ) laser crystal with dimensions up to 25 mm × 15 mm × 10 mm was grown by the Kyropoulos method. The crystal structure was identified as β-KEr 0.1 Yb 0.9 (WO 4 ) 2 by XRD analysis. Through TG-DTA curves, the melting point and transition point of the crystal were determined to be 1058 and 1031 °C, respectively. Infrared spectrum and Raman spectrum were measured, and the vibration frequencies of infrared and Raman active modes for the crystal were assigned. The absorption cross section is 3.1 × 10 −20 cm 2 at chief peak of 981 nm with the absorption line width of 26 nm. Based on the Judd-Ofelt theory, the intensity parameters Ω λ ( λ =2,4,6) calculated were: Ω 2 =16.34 × 10 −20 cm 2 , Ω 4 =4.18 × 10 −20 cm 2 , and Ω 6 =1.26 × 10 −20 cm 2 . There was a strong emission peak near 1533 nm and the emission line width at the main peak at 1533 nm run up to 55 nm with the emission cross section of 3.47 × 10 −20 cm 2 . These optical parameters indicated the potential of this crystal used as an excellent laser material for 1540 nm nearby human-eye safe.