Growth, thermal and spectral properties, and laser performance of Nd3+:CNAGS crystal

Abstract

A Nd³⁺-doped Ca₃Nb(Al_0.5Ga_0.5)₃Si₂O₁₄ (Nd:CNAGS) crystal with dimensions 50 × 80 × 16 mm³ was grown for the first time using the Czochralski (Cz) method as a potential material for ultrafast laser application and elastic optical modulators. The thermal expansion coefficients in different directions show a small difference, which means that the crystal expands more uniformly and could reduce the internal stress concentration when the temperature changes. The specific heat of Nd:CNAGS in the temperature range of 25–300 °C was in the range of 0.632–0.988 J g⁻¹ K⁻¹. The thermal conductivity of the crystal is anisotropic, and the thermal conductivity in the z direction increases with the increase of temperature and is obviously greater than that in the x direction. The optical properties of the crystal, including absorption, transmission, and fluorescence spectra, have been systematically analyzed; the strongest absorption peak with a full width at half-maximum (FWHM) of 19 nm is centered at 805 nm wavelength, and the broad emission band with a peak at 1066 nm has an FWHM of 16 nm. The experimental line strength, the calculated spectral line intensities, the spontaneous radiation probability, the fluorescence branching ratio, and the radiation lifetime are obtained using the Judd–Ofelt (J–O) theory. A 1.06 μm continuous-wave (CW) laser output was realized using the Nd:CNAGS crystal. The maximum output power at 1.06 μm wavelength is 1.54 W at an incident pump power of 12.87 W under an output coupler of 5% along the x-axis direction, corresponding to an optical-to-optical conversion efficiency of 11.97% and a slope efficiency η of 12.28%.