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

Ytterbium-doped Sr-5(PO4)(3)F (S-FAP) has been shown to be a useful material for diode pumping, since it displays high gain, low loss, and a long radiative lifetime. One of the issues with S-FAP is that it has a relatively narrow absorption bandwidth (similar to 5 nm) at 900 nm, the diode-pumping wavelength, while the diode's output bandwidth can be large (similar to 10 nm), By changing the host slightly, the absorption feature can be broadened to better match the pump bandwidth. Four mixed crystal boules of Yb3+:Sr5-xBax(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 increasing barium concentration from 4.7 nm to a maximum of 15.9 nm, Emission 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-signal gain. The absorption feature's homogeneity was probed using a tunable pump source which qualitatively showed that the barium-broadened lines mere at least partly inhomogeneous, Each of these materials lased with a variety of output couplers. This family of materials was found to provide suitable laser hosts where a broader absorption and/or emission bandwidth is desired.