Growth of Cr,Yb:YAG single crystals for self-Q-switched monolithic solid-state lasers

The saturable absorbers play key role in passively Q-switched lasers, and Cr4+-doped crystals present attractive advantages for Yb:YAG lasers. At present the major problem is the low doping concentration of Cr4+ and the effective way to promote Cr3+→Cr4+ conversion. From this view, we introduce divalent additives Ca2+ and Mg2+ as charge compensators to ensure the charge state of Cr4+ in the tervalence environment of Yb:YAG. The results reveal that this method can promote Cr3+→Cr4+ conversion effectively and an optimal CaO/MgO ratio is 1:4. The corresponding Cr0.01at.%,Yb5at.%:YAG single crystals present enhanced absorption coefficients and fluorescence intensity at 941 nm and 1030 nm, and decreased fluorescence lifetimes and decay curves than Yb:YAG. The thermal expansion coefficient and laser damage threshold of Cr,Yb:YAG single crystal are approaching the YAG host material. The results show that Cr,Yb:YAG crystal has good potential for self-Q-switched monolithic solid-state lasers. •The Cr0.01at.%,Yb5at.%:YAG single crystals of different CaO/MgO ratios as charge compensators by the Czochralski method.•The Ca2+ and Mg2+ can effectively force Cr3+ convert to Cr4+, and an optimal CaO/MgO ratio of 1:4 can obtain the highest concentration of Cr4+.•The increase of the concentration of Cr4+ can enhance the absorption coefficients of Cr,Yb:YAG single crystals at 941 nm and 1030 nm.•The thermal expansion coefficient and laser damage threshold of Cr,Yb:YAG single crystal are identified as 8.68 × 10−6/°C and 100 ± 5 J/cm2 respectively, which are approaching the values of YAG host material.