High-power diode-pumped solid-state 2 micron lasers

Abstract

Brightness scaling of diode-bar end-pumped solid-state lasers producing efficient output radiation in the 2µm wavelength region is investigated. Problems and strategies for power scaling diode-bar end-pumped lasers in the 2µm region are also discussed.
Thermal lens measurements 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 M₂ 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.

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