为了研究点衍射干涉仪中针孔的横向离焦与轴向离焦对衍射光的强度与衍射参考波面误差的影响，基于菲涅耳衍射理论，建立了会聚光束经针孔衍射的数学模型，提出了将针孔衍射光的强度与衍射波面误差相结合以分析针孔衍射波前的方法，并综合考虑了会聚光束F 数、针孔直径等参数的影响。研究表明：会聚光束F 数越大，衍射光强度与波面误差越小；横向离焦的距离应小于艾里斑半径与针孔半径之差；横向离焦的允许范围与波长和F 数成正相关，与针孔直径成负相关；当光束F=10 时，在0~35 mm 横向离焦范围内，直径1 mm 以内的针孔可以全程满足波面误差峰谷(PV)值优于0.1λ 的要求；可以通过调整轴向离焦来调整参考光的强度，并且针孔直径越小调整越灵敏；选择直径小于艾里斑半径的针孔可以保证衍射波前误差PV 值优于10-2 λ ，测试光的强度控制在针孔有效衍射光强的1/10附近。仿真结果为设计点衍射干涉仪和分析其精度提供了理论和数据参考。

In order to study the effect which the lateral and axial defocus of pinhole have on diffraction intensity and reference wavefront quality in point diffraction interferometer, a mathematical model of convergent beam diffracted by a pinhole is established based on Fresnel diffraction theory. A novel method is proposed which combines the diffraction intensity with the peak value of diffraction wavefront error to analyze the wavefront diffracted by pinhole. F number of the converging beam and diameter of the pinhole are also taken into consideration. The results show that either diffraction intensity or reference wavefront error varies in inverse proportion to the F number of converging beam. The amount of lateral defocus should be less than the difference value of the radius of Airy disk and the pinhole. The acceptable value of lateral defocus is directly proportional to the wavelength and F number while being inversely proportional to the pinhole′s diameter. With the beam F number of 10 and the lateral defocus ranging from 0 to 35 mm, the pinhole with a diameter less than 1 mm can satisfy the requirement that the peak valley (PV) value of wavefront error should be less than 0.1 λ . The reference wavefront intensity can be changed by adjusting the axis defocus. The smaller the diameter of the hole is, the more sensitive the change is. A pinhole with a diameter less than the radius of Airy disk can make sure that the peak value of diffraction wavefront error is less than 0.01 λ and the test wavefront intensity should be controlled around one tenth of the effective diffraction intensity of the pinhole. The simulation results provide a theoretical basis and data reference for the design of point diffraction interferometer and its accuracy analysis.