A master oscillator power amplifier (MOPA) laser with a controllable gain distribution was built up in our experiment. With the gain guiding effects, the final beam quality of the MOPA system with two amplification stages was near-diffraction-limited compared with in the master oscillator, and the total extraction efficiency of amplifier stages was up to 44% corresponding to a 107 W laser output. The enhancement of the beam quality during the amplifying process was also observed in the other two MOPA lasers with the optimal gain adjusting, a MOPA laser containing a seed laser and four amplifier stages, and another MOPA laser containing a Nd:yttrium aluminum garnet acoustic-optic cavity dump pulsed seed laser and four amplifier stages. It has been shown for the first time to our knowledge that not only the power scaling can be realized in the MOPA configuration, but the beam quality can be enhanced as well because of the gain guiding effects.
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