We report on an efficiency increase for blue laser diode (LD) pumped continuous-wave (CW) Ti:sapphire lasers. We theoretically analyzed our experimental results and previous research and clarified the reliability of our theoretical model. Furthermore, we analyzed the optical-to-optical conversion efficiency of blue LD pumped CW Ti:sapphire lasers by using this theoretical model. As a result of the analysis, we found that the highest efficiency of 22.4% could be achieved with blue LD pumped CW Ti:sapphire lasers by using high intensity pumping and through our optimizations. To the best of our knowledge, this efficiency reaches the equivalent efficiency of the highest efficiency of green LD pumped CW Ti:sapphire lasers. According to previous research, improving blue LD pumped Ti:sapphire laser efficiency is challenging. Nevertheless, our analysis clarified that efficiency increases for blue LD pumped CW Ti:sapphire lasers can be achieved.

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.

We quantified the influence of 445 nm pumping for the efficiency of Ti:sapphire laser. Moreover, theoretical analysis shows that efficiency increasement is achieved by high intensity pumping even at 445 nm pumping.

we analyzed theoretically the efficiency of blue laser diode pumped Ti:sapphire laser. We theoretically improved efficiency of Ti:sapphire laser under Pump-band Fraction[1] and Pump-induced Loss[2] by high intenticy pumping.