[19p-431B-1~18] 3.5 Laser system and materials

[19p-431B-15] Discussion on the Secondary Phase at Grain Boundaries in Transparent Yb:FAP

〇Yoichi Sato¹, Takunori Taira¹ (1.Inst. Mo;. Sci.)

Keywords:Anisotropy, Ceramic laser, Orientation control

We succeeded the suppression of the secondary phases in Yb-doped fluoroapatite (Yb:FAP) ceramics by tuning the Yb³⁺-doping concentration in raw powders. Even though the orientation-controlled Yb:FAP ceramics already performed the high Figure of Merits for giant microphotonics, the secondary phase at grain boundaries inside Yb:FAP ceramics limits the useful area that can generate the stimulated emission. As a result, the maximum output power of Yb:FAP ceramics still remains 2.3 kW due to the narrow clear aperture of 130 µm in dia. Energy dispersive x-ray spectra shows that the ratio of Ca/P of the main matric and secondary phase are 5:3 and 3:2, respectively, which indicates that the main composition of the secondary phase can be tri-calcium phosphate ( Ca₃(PO₄)₂, TCP). Since doped Yb³⁺-ions substitutes Ca²⁺ in fluoroapatite, there can be plenty of vacancy at Ca²⁺-site for the sake of charge compensation, which can be the causes thermal decomposition of apatite crystals to TCP.