高功率固体激光装置中空间滤波器小孔可将光束中非线性增长较快的空间频率成份滤除，改善由光学元件缺陷导致的光束质量下降，因此小孔的尺寸设计是关系滤波效果的关键因素之一。从抑制非线性最快增长频率出发，对神光Ⅲ原型装置中非线性增长最严重的助推放大级非线性增益进行了理论计算，分析了不同频率成份非线性增长的特点，根据分析结果讨论了该级空间滤波器滤波小孔的尺寸设计要求。分析了影响小孔尺寸设计的两个主要因素：等离子体堵孔效应及低频环效应，并讨论了相应尺寸设计要求。根据分析结果，以神光Ⅲ原型装置助推放大级为例对空间滤波小孔尺寸设计方案进行了讨论。

The spatial filter pinhole in high power solid state laser is used to filter the spatial frequency whose nonlinear growth is fast to improve the beam quality that is destroyed by optical elements defect. Thus the diameter of pinhole is the key factor related to the filtering effect. The nonlinear growth in boost amplifier of Sheng Guang(SG)Ⅲ prototype is calculated and the characteristics in different spatial frequency are analyzed. Based on the simulation results, the pinhole diameter design in boost amplifier is discussed. The pinhole closure caused by plasma and the low frequency circle in near field in pinhole diameter design is analyzed. According to the simulation results, the pinhole diameter design principle in boost amplifier of SGⅢ prototype is discussed.