Laser properties of Yb3+-doped Sr5(PO4 )3F crystals

The authors believe that Yb³⁺-doped Sr₅(PO ₄)₃F (Yb:S-FAP) is particularly well adapted for low to medium power laser applications that are sensitive to overall efficiencies. Yb:S-FAP has a relatively low pump saturation intensity of 2.0 kW/cm² which is well suited to diode pumping since the ground state can be readily bleached. This spatial bleach wave pumping is required for efficient operation of a quasi three level laser and is also well suited for efficient amplifier energy extraction. In contrast, Yb:YAG has a pump saturation intensity of 28 kW/cm², which is more difficult to exceed with commonly available diode arrays; although, Yb:YAG does offer significantly better thermal properties. Yb:fiber lasers use a different approach to the ground state bleaching issue by confining the pump field to the relatively small fiber core. Unfortunately, this approach is not readily scalable to large output energies. The remainder of the paper focuses on some recent experimental results obtained in the process of developing efficient diode pumped Yb:S-FAP laser systems capable of efficiently providing ~1 J at 1047 nm