Abstract:

For high power lasers, the thermal effect imposes a limit on the power density dissipated inside the gain element, while it can be reduced by increasing the size of gain medium, which enhances heat dissipation. However, when aspect ratio of the gain medium increases, spontaneous fluorescence can be drastically amplified. 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 a 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. Here, the 5% Sm:LuAG/1% Nd:LuAG (in atom) cladding laser ceramics (φ56.0 mm×4.8 mm) using commercial Lu₂O₃, α-Al₂O₃, Nd₂O₃ and Sm₂O₃ powders as raw materials were fabricated by vacuum pre-sintering at 1825 ℃ for 20 h and HIP post-treatment at 1750 ℃ for 3 h with TEOS and CaO as sintering additives. The in-line transmittance of the gain area is 81.5% at 1064 nm, while that of the cladding area is 78.6% at 808 nm.

Key words: laser ceramic, cladding composite structure, Sm:LuAG/Nd:LuAG, microstructure, optical property