Growth, thermal and spectral properties, and laser performance of Tm3+:CNGS crystal

Abstract

New composite functional crystals of Tm³⁺:Ca₃NbGa₃Si₂O₁₄ (Tm³⁺:CNGS) were successfully grown by the Czochralski (CZ) method. The structural, thermal and spectral properties of Tm³⁺:CNGS crystals were investigated. The laser output of a Tm³⁺:CNGS crystal in the 2 μm band was studied for the first time. The results showed that Tm³⁺:CNGS achieved a maximum output of 740 mW at a pump power of 5 W, and the slope efficiency and light-to-light conversion efficiency reached 17.07% and 14%, respectively. The thermal properties are presented, and the coefficient of linear thermal expansion of Tm³⁺:CNGS increased with respect to that of a pure CNGS crystal in the Z-axis direction, which may have been due to a change in the bulk density of the oxygen dodecahedron in the X-axis direction after partial replacement of the rare earth ions. In addition, the specific heat, thermal diffusivity, and thermal conductivity of Tm³⁺:CNGS slightly increased in comparison with those of the undoped CNGS crystal. The absorption spectra of Tm³⁺:CNGS had a strong peak at 793 nm, and its absorption cross-section was 5.01 × 10⁻²¹ cm². The fluorescence spectra at room temperature had a full width at half maximum (FWHM) of 164 nm and a peak wavelength of 1888 nm, and the lifetime of the ³F₄ upper energy level of the laser was 2.345 ms. Its good thermal properties, large emission linewidth, and ease of growth indicate that a Tm³⁺:CNGS single crystal could have the potential to be a good laser gain medium.