Thermo-optic effects in Ho:KY(WO 4 ) 2 thin-disk lasers

Thin (~250 µm) crystalline layers of monoclinic Ho3+-doped KY(WO4)2 grown by the liquid phase epitaxy method on (010)-oriented undoped KY(WO4)2 substrates are promising for the development of thin-disk lasers at ~2.1 µm. Using a single-bounce pump geometry, 3 at.% and 5 at.% Ho:KY(WO4)2 thin-disk lasers delivering output powers of >1 W at 2056 nm and 2073 nm are demonstrated. The laser performance, beam quality and thermo-optic aberrations of such lasers are strongly affected by the Ho3+ doping concentration. For the 3 at.% Ho3+-doped thin-disk, the thermal lens is negative (the sensitivity factors for the two principal meridional planes, MA(B), are −1.7 and −0.7 m−1/W) and astigmatic. For higher Ho3+ doping (5-10 at.%), the effect of upconversion and end-bulging of the disk enhances the thermo-optic aberrations leading to a deteriorated laser performance.