Characterization ofYb3+:Sr5-xBax(PO4)3F crystals for diode-pumped lasers

摘要

Ytterbium-doped Sr5(PO4)3Fn(S-FAP) has been shown to be a useful material for diode pumping, sincenit displays high gain, low loss, and a long radiative lifetime. One ofnthe issues with S-FAP is that it has a relatively narrow absorptionnbandwidth (~5 nm) at 900 nm, the diode-pumping wavelength, while thendiode's output bandwidth can be large (~10 nm). By changing the hostnslightly, the absorption feature can be broadened to better match thenpump bandwidth. Four mixed crystal boules of Yb3+:Sr5-xnBax(PO4)3F were grown by thenCzochralski method with x=0.25: 0.5, 1, and 2. The bandwidth of then900-nm absorption feature was found to grow with increasing bariumnconcentration from 4.7 nm to a maximum of 15.9 nm. Emission spectranshowed a similar bandwidth increase with barium content from 4.9 nm to anmaximum of 10 nm. Emission cross sections for these materials werendeduced by the methods of reciprocity, the Einstein method, andnsmall-signal gain. The absorption feature's homogeneity was probed usingna tunable pump source which qualitatively showed that the bariumnbroadened lines were at least partly inhomogeneous. Each of thesenmaterials lased with a variety of output couplers. This family ofnmaterials was found to provide suitable laser hosts where a broadernabsorption and/or emission bandwidth is desired