Abstract: A concentration gradient Yb∶YAG laser crystal with a size of 180 mm×81 mm×16 mm was grown by horizontal directional crystallization (HDC) method. Four crystal pieces with the size of 40 mm×40 mm×7 mm and 70 mm×70 mm×7 mm (two pieces for each size) were taken from the shoulders and tails of the single crystal plate, respectively. A 632 nm laser and a polarizing stress meter was used to characterize the samples’ optical properties. From the results, it can be seen that compared to the crystals near the crucible, the crystals near the surface are more transparent, with no scattering light path, and showing lower and more uniform stress. The crystal was also subjected to absorption spectra measurement, and its absorption coefficient at 935 nm wavelength was used to calculate the doping concentration of Yb³⁺ at different positions in the crystal. It was found that the Yb³⁺ doping concentration in laser crystal plates with a size of 40 mm×40 mm×7 mm gradually increased along the crystal growth direction, with a concentration gradient of approximately 0.42%/cm. The Yb³⁺ doping concentration in laser crystal plate with a size of 70 mm×70 mm×7 mm remains almost unchanged, which is approximately 4.50%.

Key words: concentration gradient, spectral property, Yb∶YAG, horizontal directional crystallization method, laser crystal