A high-beam-quality diode-pumped neodymium-doped yttrium aluminum garnet (Nd:YAG) active mirror laser amplifier was demonstrated. The size of the Nd:YAG crystal was 48 mm?×?42 mm?×?11 mm with 0.6 at.% Nd doped. When the pump energy was 26.8 J and the input energy was 0.3 J, the output pulse energy r