Modeling of High-Power Continuous-Wave Tm:YAG Side-Pumped Double-Clad Waveguide Lasers

A plane-wave model accounting for cross-relaxation, upconversion, ground-state depletion, and gain saturation in continuous-wave laser systems is applied to side-pumped Tm:YAG double-clad planar waveguides. The temperature profile due to high-power pumping, and the delivery and absorption efficiencies of proximity-coupled diode bars, are also calculated. The theoretical performance is found to be a good fit to the experimental results, which show 15-W output at 2 m from 43 W of diode pump power. The output channels for the absorbed power are quantified, and it is shown that upconversion limits the gain and, hence, the size of the output coupling that can be used in such lasers. The same theory is then used to design a very compact waveguide laser capable of delivering 100 W of output power.