High-power diode-pumped solid-state 2 micron lasers
Brightness scaling of diode-bar end-pumped solid-state lasers producing efficient output radiation in the 2 μm wavelength region is investigated. Problems and strategies for power scaling diode-bar end-pumped lasers in the 2μm region are also discussed. Thermal lens measure ments on Tm3+:YAG and Tm3+:(Lu,Y)AG were made. Thermal lens dependency on resonator loss is observed and attributed to heating from upconversion. High-power room temperature diode-bar end-pumped Tm3+:(Lu,Y)AG were developed. Efficient high power operation of the Tm3+:YAG laser producing 14.2W of output power at 2.013μm for 53.4W of incident pump power is demonstrated with M(2) values of 1.3 in orthogonal planes. The laser was then linearly polarised and compared with a similar laser using a scheme to compensate for the loss caused by thermally induced de-polarisation. Before the de-polarisation loss prevented lasing operation an output power of 8.4W was observed. Using the compensation scheme, the laser produced 11.5W of output power and was limited by pump power. The uncompensated de-polarisation loss was >5% reducing to <0.4% for the compensated laser. A high power Tm3+:(Lu,Y)AG laser producing 18W of output power at 2.022μm was demonstrated and compared with a Tm3+:YAG laser. High-power intracavity pumped Ho3+:YAG lasers were developed. A collinearly intracavity pumped Ho3+:YAG laser producing 8.4W of output power is demonstrated though application of the brightness scaling strategy was difficult to implement. A non-collinearly intracavity pumped laser showing 1.6W of output power is reported but showed alignment instability and was hard to replicate. Intracavity pumping schemes are discussed. A Tm3+:silica fibre laser produced 14.2W of output at 1.98μm for 38.3W of launched pump power with a slope efficiency of ~36%. This was the highest reported power from a Tm3+:silica fibre laser to the author's knowledge. A tunable Tm3+ fibre laser showed > 1.8W output power across a tuned wavelength range of 1870-2030 nm.