Abstract: For high power lasers, the thermal effect imposes a limit to the power density dissipated inside the gain element, while it can be reduced by increasing the size of the gain medium, and it will enhance heat dissipation. However, when the aspect ratio of the gain medium is large, spontaneous fluorescence will be amplified to very high power. Transverse propagation of spontaneous fluorescence induces amplified spontaneous emission, triggering detrimental parasitic oscillations. A promising solution involves applying cladding layers to the lateral surfaces of gain media to absorb stray radiation. For high repetition rate nanosecond high power solid-state lasers, it is essential to choose gain media with moderate saturation flux. Among these, Nd:LuAG transparent ceramics have shown significant potential due to their outstanding optical, mechanical, and thermodynamic properties. Additionally, Sm:LuAG transparent ceramics, with their high absorption coefficient at 1064 nm, excellent theoretical optical transmittance at 808 nm, and a refractive index similar to that of Nd:LuAG, have emerged as one of the best materials for cladding Nd:LuAG laser ceramics. The commercial Lu₂O₃, α-Al₂O₃, Nd₂O₃ and Sm₂O₃ powders were used as raw materials. The 5% Sm:LuAG/1% Nd:LuAG (in atomic) cladding laser ceramics (ϕ56.0 mm×4.8 mm) were fabricated by vacuum pre-sintering at 1825 ℃ for 20 h and HIP post-treatment at 1750 ℃ for 3 h using TEOS and CaO as sintering additives. The in-line transmittances of the gain area are 81.5% at 1064 nm, and the cladding area is 78.6% at 808 nm.

Key words: laser ceramics, cladding composite ceramics, Sm:LuAG/Nd:LuAG, microstructure, optical properties