High-Efficiency Continuous-Wave Ti:Sapphire Laser with High-Intensity Pumping Using a Commercially Available Crystal

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Despite the importance of improving the efficiency of lasers in order to expand their utility range, the improvement of the efficiency of Ti:sapphire lasers has not progressed due to their high crystal losses. Therefore, we improved the efficiency of CW Ti:sapphire lasers by high-intensity pumping, which is one of the most effective methods of suppressing the efficiency reduction due to losses. Using a easily commercially available 0.25 wt.%, figure of merit (FOM) 200 Ti:sapphire crystal, optics and a pump source, we achieved an optical-to-optical conversion efficiency of 32.4% with a slope efficiency of 42.5% at an incident pump power of 5.0 W which corresponds the maximum pumping intensity of 860 kW/cm2. Furthermore, we ensured the reliability of our theoretical analysis by reproducing the experimental results. From this reliable theory, double-pass pumping and increasing the pump power to 25 W resulted in the highest optical-to-optical conversion and slope efficiencies for the incident pump power of 55.9% and 59.6%, respectively, at a high intrinsic residual loss of 4.0%. Even if losses doubled or deviated from the optimum condition for the highest efficiency, the efficiency reduction due to these factors was only a few percent. These results show that with high-intensity pumping, lasers with efficiencies well exceeding half of the quantum limit can be achieved even if all components, including Ti:sapphire crystals, are easily commercially available.