Beam quality enhancement in side-pumped master oscillator power amplifier system

The beam quality enhancement in a side-pumped master oscillator power amplifier is experimentally realized by a novel method of spherical aberration compensation. Numerical calculations show that the positive spherical aberration is reversed to a negative one after the beam focus; in addition, the negative spherical aberration can be compensated by another amplifier. A two-stage side-pumped Nd:YAG master oscillator power amplifier has been developed. Seed beam from the oscillator with 42 W CW output power and a beam quality of 1.48 has been boosted up to 74 W after the first amplifier, with a degraded beam quality of 1.80. As expected, the output beam quality has been enhanced to 1.40 after the second amplifier. The experimental results verify the validity of the method to improve the beam quality in the process of laser amplification.