Crystal growth, structure, optical properties and laser performance of new tungstate Yb:Na2La4 (WO4)7 crystals

The 2 at.% and 10 at.% Yb:Na2La4(WO4)(7) crystals with dimensions of 0 21 x 24 mm(3) and 0 24 x 28 mm3 were grown by the Czochralski method. The crystal growth, spectroscopic properties and laser performances of the two crystals were investigated. The peak absorption cross-sections of the 2 at.% and 10 at.% Yb:Na2La4(WO4)(7) crystals are 1.51 x 10(-20) cm(2) and 1.74 x 10-20 cm2 along a-polarization, as well as 1.61 x 10(-20) cm(2) and 1.34 x 10(-20) cm(2) along 7Cpolarization, respectively. The emission cross sections calculated by Fuchtbauer-Ladenburg (FL) method along aorientation are 1.45 x 10(-20) cm(2) and 2.31 x 10(-20) cm(2) at 10(12) nm for the two crystals, respectively. The reciprocity method (RM) was adopted to calculate the emission cross-sections for compassion, and the values at 1012 nm for the two crystals are 0.27 x 10(-20) cm(2) and 0.34 x 10(-20) cm(2), respectively. Strong re-absorption effect exists in the crystals, and the analysis of the re-absorption probabilities shows that the crystal with as high as 10 at% Yb3+ concentration has more serious re-absorption effect than many other Yb-doped crystals. The lifetimes of the excited state of Yb3+ in the two crystals were measured and fitted to be 0.392 ms and 0.422 ms, respectively. Based on the absorption and emission spectra, the important laser potential parameters, including the minimum inversion fraction beta min, the saturation pump intensity Isat, the minimum pump intensity Imin and gain emission cross-sections were evaluated and results indicates that Yb:Na2La4(WO4)(7) are candidate lasing mediums. The laser experiments were also performed and continuous-wave (cw) laser actions were demonstrated with the c-cut uncoated crystal samples in a plane-concave cavity, end pumped by a 977 nm laser diode. The maximum output powers are respectively 1.15 W and 0.85 W for the 2 at.% and 10 at.% Yb:Na2La4(WO4)(7) crystals, along with the corresponding slope efficiencies of 17.24% and 12.35% when the transmittance of the output coupler is 5%. All the results indicate that the new tungstate Yb:Na2La4(WO4)(7) crystal is a good laser medium.