Photoconductivity in Yb-doped materials at high excitation densities and its effect on highly Yb-doped thin-disk lasers

Transient Yb²⁺ states the role of permanent Yb²⁺ states is discussed. Investigations on Yb:YAG single crystals grown in reducing atmosphere reveal that the magnitude of photocurrent is reduced by annealing the sample. This result points towards an involvement of permanent Yb²⁺ states in the photoconductivity mechanism. To further examine the influence of Yb²⁺-ions, samples with Si⁴⁺ co-doping are presently investigated which are known to stabilize the Yb²⁺ valency.In Yb-doped Lu₂O₃ and YAG thin-disk lasers a decrease in laser efficiency with increasing inversion level has been reported. The observed non-linear energy losses display a similar dependency on excitation density and doping concentration as the photoconductivity measurements. Therefore a correlation between both phenomena is suggested as they may be caused by the same mechanism.