In a recent breakthrough published in Optics & Laser Technology and Infrared Physics & Technology, a research team led by Prof. CHENG Tingqing at the Hefei Institutes of Physical Science of the Chinese Academy of Sciences have introduced a novel low-thermal-effect gradient-doped crystal to tame thermal effects and improve brightness of high-power end-pumped Nd:YAG lasers.
End-pumped solid-state lasers typically use uniformly doped crystals, which develop significant temperature gradients and thermal stresses under high pump power due to the axial absorption decay of pump power. These effects not only limit maximum pump power, but also degrade beam quality and conversion efficiency.
In this study, the researchers devised a numerical model for crystals whose neodymium concentration gradually increases along the rod, providing a theoretical basis for optimizing the concentration distribution and growth of novel gradient-doped crystals.
Theoretical analysis and experimental validation showed that the optimized gradient-doped crystal markedly extends the effective absorption length and smooths longitudinal pump energy absorption distribution, reduces thermal gradients and end-face deformation, and lengthens the thermal-lens focal length. Under continuous-wave pumping, the crystal maintained a linear output-power rise and achieved conversion efficiencies above fifty percent.
Building on these results, the team developed a high-brightness, electro-optically Q-switched laser. By matching a plano-convex cavity design and pump-spot size to the dopant gradient, they controlled the intracavity gain intensity and mode volume, yielding average powers in the double-digit watt range, pulse peak powers approaching the megawatt scale under near-diffraction-limited beam quality—together setting a new brightness record for single-end-pumped, single-rod Nd:YAG lasers.
The work offers a way toward the design of next-generation, high-brightness laser sources for industrial, medical, and scientific applications.
Temperature, stress, and strain distributions in the axial cross section of gradient-doped crystals. (a) 0.39 ~ 0.80 at.% crystal; (b) 0.17 ~ 0.38 at.% crystal; (c) 0 at.% + 0.17 ~ 0.38 at.% crystal. (Image by MA Tianyu)
