Near-diffraction-limit 1-kHz sub-nanosecond diode-end-pumped Nd:YAG laser amplifier via self-compensating spherical aberration

A high-beam-quality 1-kHz sub-nanosecond Nd:YAG master oscillator power amplifier (MOPA) system based on diode end pumping is demonstrated. Based on detailed theoretical analysis on thermal effects in the gain medium, especially the spherical aberration which played the major role in beam degradation, a simple and effective compensation scheme was designed for the experiment. While the single pulse energy was amplified from 80 μJ (oscillator) to 2.72 mJ (amplifier, 34 times magnification), the beam quality factor (M2) was improved from 1.21 to 1.14 at the same time. The evolution of pulse duration with the increase of pump power was also investigated. The output pulse width of 454 ps corresponded to the peak power of 6 MW, the highest in kHz-level end-pumped single-stage Nd:YAG amplifiers up to now. The MOPA system demonstrated excellent operating stability, with the peak-to-peak and root-mean-square (RMS) power fluctuation of 2.78 % and 0.54 %, respectively.