Power scaling potential of continuous-wave Cr:LiSAF and Cr:LiCAF lasers in thin-disk geometry

Continuous-wave (cw) output power from Cr:Colquiriite lasers is currently limited to the 3 W level due to weak thermal and mechanical properties of the Colquiriite host that hinders power scaling efforts. Thin-disk (TD) geometry, which has enabled record power levels in Yb:YAG gain media, has not yet been thoroughly studied for Cr:Colquiriites. In this work, we have numerically investigated the cw lasing potential of TD Cr:LiSAF and Cr:LiCAF lasers in detail. Our analysis has shown that, due to their low thermal conductivity and high susceptibility to temperature quenching of fluorescence lifetime, TD lasers based on Cr:LiSAF will require usage of ultrathin (100 μm thick) crystals with large diameters (15-25 mm), which will be difficult to prepare/handle due to its glass-like thermomechanical strength. Assuming such TD crystals could be produced, we estimate that cw powers above 15 W might be feasible from Cr:LiSAF thin-disk lasers (TDLs) pumped by a 100 W red diode. As an alternative, usage of Cr:LiCAF, which is the strongest member of Cr:Colquiriites in terms of thermomechanical properties, enables tighter focusing of a pump beam on the TD, which in turn facilitates adoption of smaller-diameter samples (10 mm). We have estimated that, when the thermally stronger c axis is used for heat extraction and the a axis is used for lasing, cw powers exceeding 30 W could be achieved from Cr:LiCAF TDLs at an incident pump power of 100 W. On the other hand, our model shows that the small signal gain that could be achieved via cw pumping of Cr:Colquiriite TD elements is below 0.5%. Hence, the aforementioned performance requires usage of high-quality factor cavities with minimal intracavity losses.