Extremely efficient, high beam quality second harmonic generation using a thin-disk regenerative amplifier

We report on a second harmonic generation (SHG) 5.79 ps, 1 MHz green laser system based on a 145 W homemade Yb:YAG picosecond thin-disk regenerative amplifier. To achieve an extremely efficient SHG process, we employed the spatial-temporal nonlinear unidirectional pulse propagation equation (UPE) to optimize the efficiency in high-power picosecond lasers. The lengths of lithium triborate (LBO) crystals, infrared laser intensities, and crystal temperatures were systematically optimized. The resulting 515 nm laser generates an average power of 107.7 W with the highest conversion efficiency of 75 % and a near-diffraction-limited beam quality, with an M2 factor of 1.14. To the best of our knowledge, it is the highest conversion efficiency achieved based on a high-power thin-disk laser to date. Furthermore, with the third-harmonic generation at 343 nm, the laser system achieved 65 W of average power and 44.8 % of conversion efficiency.