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

Abstract

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.

A low-cost approach to diode-pumped Ti:Sapphire resonators with Watt-level output

“…Although this result demonstrated good slope efficiency, approaching that expected from a 532 nm pump [14], most applications of Ti:sapphire demand near-diffraction limited output which we demonstrate in the next section by inserting an intracavity slit.…”

A low-cost approach to diode-pumped Ti:Sapphire resonators with Watt-level output

“…Although this result demonstrated good slope efficiency, approaching that expected from a 532 nm pump [14], most applications of Ti:sapphire demand near-diffraction limited output which we implement in the next section by inserting an intracavity slit.…”

Influence of High-Intensity Pumping on Gain Medium Temperature Increase and Laser Mode Tunability in a Hemispherical Short Cavity

“…In the theoretical analysis, we used quasi-three-level (quasi-four-level) laser rate equations with CW pumping, which include the spatial distribution of the pump and laser beams [17,[38][39][40][41]. In the case of quasi-three-level (quasi-four-level) lasers, as in the case of four-level lasers, for simplicity, we define the normalized incident pump power F, which is dimensionless with respect to the incident pump power on the gain medium P p , as…”

“…For hemispherical short-cavity CW Yb:YAG lasers, optical conversion efficiencies exceeding 75% for the incident pump power have also been achieved [15]. In addition, optical-to-optical conversion efficiencies exceeding 31% for the incident pump power have been achieved for T:sapphire lasers despite the use of commercially available high-loss Ti:sapphire crystals [16,17]. Using a theory that quantitatively reproduces the experimental results of Ti:sapphire lasers, it has been shown that even under conditions of a high intrinsic residual loss of 4%, an optical-to-optical conversion efficiency of 55.9%, approaching the quantum limit of Ti:sapphire lasers, can be achieved by using high-gain by high-intensity pumping [17].…”

“…In addition, optical-to-optical conversion efficiencies exceeding 31% for the incident pump power have been achieved for T:sapphire lasers despite the use of commercially available high-loss Ti:sapphire crystals [16,17]. Using a theory that quantitatively reproduces the experimental results of Ti:sapphire lasers, it has been shown that even under conditions of a high intrinsic residual loss of 4%, an optical-to-optical conversion efficiency of 55.9%, approaching the quantum limit of Ti:sapphire lasers, can be achieved by using high-gain by high-intensity pumping [17]. To the best of our knowledge, as shown in Table 1, the efficiency of CW Yb lasers using high-gain by high-intensity pumping is almost equal to or higher than the efficiency using other technologies [8][9][10][11][12][18][19][20][21][22][23].…”