Characterization of Yb3+: Sr5-xBax(PO4)(3)F crystals for diode-pumped lasers

Ytterbium-doped Sr-5(PO4)(3)F (S-FAP) has been shown to be a useful materia l for diode pumping, since it displays high gain, low loss, and a long radi ative lifetime. One of the issues with S-FAP is that it has a relatively na rrow absorption bandwidth (similar to 5 nm) at 900 nm, the diode-pumping wa velength, while the diode's output bandwidth can be large (similar to 10 nm ), By changing the host slightly, the absorption feature can be broadened t o better match the pump bandwidth. Four mixed crystal boules of Yb3+:Sr5-xB ax(PO4)(3)F were grown by the Czochralski method with x = 0.25, 0.3, 1, and 2. The bandwidth of the 900-nm absorption feature was found to grow with i ncreasing barium concentration from 4.7 nm to a maximum of 15.9 nm, Emissio n spectra showed a similar bandwidth increase with barium content from 4.9 nm to a maximum of 10 nm, Emission cross sections for these materials were deduced by the methods of reciprocity, the Einstein method, and small-signa l gain. The absorption feature's homogeneity was probed using a tunable pum p source which qualitatively showed that the barium-broadened lines mere at least partly inhomogeneous, Each of these materials lased with a variety o f output couplers. This family of materials was found to provide suitable l aser hosts where a broader absorption and/or emission bandwidth is desired.