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

Abstract

Continuous-wave (cw) output power from Cr:Colquiriite lasers is currently limited to the 3W 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 (100μm thick) crystals with large diameters (15-25mm), 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 15W might be feasible from Cr:LiSAF thin-disk lasers (TDLs) pumped by a 100W 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 (10mm). 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 30W could be achieved from Cr:LiCAF TDLs at an incident pump power of 100W. 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.