Thermal lensing in an end-pumped Yb:KGW slab laser with high power single emitter diodes

We demonstrate that it is possible to pump an Ng-cut Yb:KGW crystal slab with up to 18W by a single emitter laser diode and still achieve a nearly diffraction limited output beam with a M(2) value below M(2) < 1.1 and optical to optical efficiencies of more than 44%. Furthermore, we have measured the focal length of thermally induced lenses in an Yb:KGW crystal slab which was end-pumped by 12 W and 18 W single-emitter diodes. We have observed that the focal lengths not only depend on the pump power and beam waists, but are also dependent on the specific diode beam profile, as well as the collimation optics. We have been able to correlate this behavior with specific patterns of the beam profile.