In order to obtain high-power laser output with excellent performance, it is a good method to adopt a laser amplification system consisting of an oscillation stage and an amplifier. In this method, the oscillator stage can determine its beam characteristics and the amplifier can determine its output power, so it can give consideration to excellent laser characteristics and high output power. In the above laser amplification system, in order to extract more power from the amplifier, the laser output from the oscillation stage usually passes through the amplifier, that is, the two-way laser amplifier. Compared with the single-pass laser amplifier, the double-pass laser amplifier can obtain greater extraction efficiency and higher output power under the same pumping conditions. However, when the pump power is high, the thermal effect of the beneficial medium in the laser amplifier will lead to the distortion of the amplified beam. In the two-way laser amplifier, the incident laser passes through the laser amplifier twice, so the deterioration of its beam quality becomes more serious than that of the single-way laser amplifier. In order to overcome this shortcoming of dual-channel laser amplifier, phase * * * yoke technology can be used in laser amplifier, as shown in figure 1. The incident laser passes through the laser amplifier once (including the oscillation stage including the total reflection mirror 1, the first laser gain medium 2 and the output mirror 3, and the amplification stage including the second laser gain medium 5), and then the phase is irradiated. The beam reflected by the phase yoke mirror 6 passes through the laser amplifier again and is reflected by the isolation beam splitter 4, which can compensate the distortion caused by thermal effect, so that the beam passing through the laser amplifier twice has good quality and high output power. However, when the pulse repetition frequency and pulse energy are high, the material used in the phase yoke mirror is easy to be damaged or its performance becomes unstable, which limits its application range. In addition, the reflection efficiency of phase yoke mirror is usually only about 50%, which leads to a great loss of laser power or energy, which is not conducive to the improvement of laser power. Therefore, it is urgent to develop a laser amplifier that can solve the problem of beam quality degradation after passing through the laser amplifier in two directions and has less input loss to laser power or energy bow.