Fabrication of Sm:LuAG transparent ceramics with different doping concentrations for cladding from co-precipitated nano-powders

For high-repetition-rate nanosecond high-power solid-state lasers, it is essential to choose gain media with moderate saturation flux. Among these materials, Nd:Lu₃Al₅O₁₂ (LuAG) transparent ceramics have shown significant potential. The thermal effect limits their power density in the gain element, but increasing the size of the gain medium can help dissipate heat. However, a large aspect ratio can lead to high spontaneous fluorescence, causing amplified spontaneous emission (ASE) and parasitic oscillations (POs). A solution is to apply cladding layers to absorb stray radiation. Sm:LuAG transparent ceramics, with high absorption at 1064 nm, good transmittance at 808 nm, and a refractive index similar to that of Nd:LuAG, are ideal for cladding Nd:LuAG laser ceramics. In this work, highly transparent Sm:LuAG ceramics were successfully fabricated first through low-temperature vacuum pre-sintering combined with high-temperature hot isostatic pressing (HIP) post-treatment using the co-precipitated Sm:LuAG nano-powders. The influences of Sm³⁺ doping concentration on the microstructure and optical transmittance of Sm:LuAG ceramics were studied. The nano-powders calcined at 1100 °C for 4 h showed dendritic agglomerations but relatively small particle sizes and high uniformity. Sm:LuAG ceramics with different doping amounts were obtained by vacuum sintering at 1550 °C for 3 h followed by HIP post-treatment at 1550 °C in an argon atmosphere at 200 MPa for 3 h. The 3 at% Sm:LuAG transparent ceramics (1.5 mm in thickness) exhibited the highest in-line transmittance of 83.9% at 808 nm, a fine grain size of 909 nm, and an absorption coefficient of 2.44 cm⁻¹ at 1064 nm, indicating that it can effectively suppress ASE and PO.