提出了一种新型的高功率激光装置的预放系统结构，采用钕玻璃再生放大结合离轴四程放大的技术途径，研究了四程放大中寄生振荡和笔形光束的产生机理和抑制措施。通过注入脉宽为3 ns，单脉冲能量小于1 nJ的1053 nm单纵模种子激光，可以获得10.3 J的近衍射极限输出，总增益大于1010，能量稳定性为2%，输出激光为近平顶分布，近场填充因子为71%，近场调制度约为1.4，91%的焦斑能量能聚焦于2倍衍射极限内。实验结果和输出性能完全满足激光装置预放系统的性能要求，验证了多程放大技术在高功率激光装置预放系统中应用的可行性。

A new laser amplifier structure based on Ndglass regenerative amplifier and off-axis four-pass amplifier is designed for high power laser facilities. The parasitic oscillation and pencil beam of the four pass amplifier are studied and a method is introduced to suppress them. By injecting a 1053 nm single longitudinal mode laser pulse with pulse duration of 3 ns and pulse energy of 1 nJ, a 10.3 J amplified pulse with a 2% shot-to-shot energy stability is obtained. The total gain of the amplifier system is over 1010. The output laser beam is a flat top profile with a 71% near field fill factor and modulation of 1.4 and 91% pulse energy can be focused into 2 times of diffraction limits. The experimental results and output performance of the amplifier system fully meet the requirements of the pre-amplifier of high power laser facilities, which shows that multi-pass amplifier can be used in high power laser facilities.