Near-diffraction-limited picosecond laser based on aberration-compensated end-pumped Nd:YAG rod amplifiers with more than 100 MW peak power and 300 W average power

A high-energy picosecond laser based on high-power diodes end-pumped Nd:YAG rod amplifiers with efficient birefringence compensation was demonstrated. The maximum linearly polarized output power from the amplifiers was up to 302 W at 250 kHz with a pulse energy of 1.2 mJ, achieving a peak power of more than 100 MW. It was found that once the issue of thermally induced birefringence in end-pumped Nd:YAG rod amplifiers is addressed, spherical aberration emerges as the primary factor responsible for beam degradation. The wavefront distortion of the amplified beam was measured, and a spherical aberration compensation plate was applied. The beam quality M² factor was improved from 1.9 to 1.2. An average power of 183 W green light was achieved through second harmonic generation with a conversion efficiency of 65%. This represents the highest, to the best of our knowledge, output with high beam quality for a picosecond Nd:YAG MOPA laser.