Co²⁺:MgAl₂O₄ saturable absorber transparent ceramics fabricated by high-pressure spark plasma sintering

Single-stage processing of high-quality transparent functional polycrystalline ceramics is desirable but challenging. In the present work, spark plasma sintering (SPS) was employed for fabrication of Co²⁺:MgAl₂O₄ saturable absorbers for laser passive Q-switching. Densification of commercial MgAl₂O₄ powders, doped via co-precipitation, was carried out by conventional SPS and high-pressure SPS (HPSPS) under pressures of 60 and 400 MPa, respectively. The presence of LiF, a common sintering additive, was detrimental to optical properties as it promoted reaction of cobalt with sulfur impurities and the formation of Co₉S₈ inclusions. Densification by HPSPS without LiF allowed to obtain highly transparent Co²⁺:MgAl₂O₄. The optical properties of samples, with doping concentrations varying between 0.01 and 0.1 at.% Co²⁺, were assessed and saturable absorption was demonstrated at ~1.5 µm wavelength, exhibiting ground-state (σ_gs) and excited (σ_es) cross-sections of 3.5×10^-19 and 0.8×10^-19 cm², respectively. Thus, it was established that HPSPS is an effective method to fabricate transparent Co²⁺:MgAl₂O₄ ceramics.