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, Nd:LuAG transparent ceramics have shown significant potential. The thermal effect limits the 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 (PO). 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 Nd:LuAG, are ideal for cladding Nd:LuAG laser ceramics. In this work, highly transparent Sm:LuAG ceramics were successfully fabricated for the first through low-temperature vacuum pre-sintering combined with HIP post-treatment using the co-precipitated Sm:LuAG nano-powders. The influences of Sm³⁺ doping concentrations on microstructure, optical transmittance of the Sm:LuAG ceramics were studied. The nano-powders calcined at 1100 ^oC for 4 h showed dendritic agglomerations, but relatively small particle size and high uniformity. Sm:LuAG ceramics with different doping were obtained by vacuum sintering at 1550 ^oC for 3 h followed by HIP post-treatment at 1550 ^oC in an argon atmosphere under 200 MPa for 3 h. The 3at.% Sm:LuAG transparent ceramic (1.5 mm 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.