Optical properties of transparent polycrystalline ruby (Cr:Al2O3) fabricated by high-pressure spark plasma sintering

Doped transparent ceramics with high optical quality can serve as materials for photonic applications such as laser gain media. In that regard, transparent polycrystalline alumina has potential for high-power applications due to its excellent physical and chemical properties, combined with unique doping possibilities. However, optical birefringence of Al₂O₃ crystals make achieving sufficiently high optical transmittance a processing challenge. In the present study, we demonstrated fabrication of highly transparent 0.5 at.% Cr:Al₂O₃ ceramics by high-pressure spark plasma sintering (HPSPS). The optical properties of these polycrystalline ruby ceramics were analyzed in order to assess possible laser operation (at 694.3 nm). The obtained ceramics exhibit high in-line transmittance (～72.5 % at 700 nm), equivalent to a scattering coefficient of 2.15 cm^?1, and characteristic ruby photoluminescence. The theoretically estimated lasing threshold and percentage of absorbed pump power indicate that such ruby ceramic lasers could operate at reasonable thresholds of 80?225 mW with short lengths of 0.5?5 mm. Thus, HPSPS is a promising method for producing laser-quality doped transparent ceramics for compact laser systems.