小F数标准球波面透镜组的F′C重合误差分析

标准球波面透镜组是光干涉计量测试凸、凹球面面形质量的重要测量器具，它能产生PUV值优于λ／20（λ=0．6328μm)的标准球面波，透镜组中末球面为标准球面。其使用特点要求透镜组的焦点F′与末面球心C重合；如果存在重合误差，则用于球面面形检验时会引入测量系统误差。推导分析了F′C的允许重合误差与透镜组F数等参量的关系，运用ZEMAX光学设计软件模拟给出系列小F数标准球波面透镜组允许的F′C重合误差，并设计实验测试方案，得到反映标准球波面透镜组F′C重合误差的干涉图，它们的波像差均小于5A。由理论分析与实验测试结果可知．F数很小(如F／1．5，F／0．75)的标准球面透镜组．F′C重合误差小于0．03mm，甚至达到微米量级。

Analysis of Coincidence Tolerance between F′ and C for the Transmission Spheres with Small F-Number

The lens assembly producing reference transmission spherical wavefront is important device for test of convex or concave spherical surfaces in an interferometer and it can offer a high-quality spherical wave and a reference spherical surface with peak-to-valley less than λ/20 (λ=0.6328 μm). According to their utility, the curvature center (C) of its last spherical surface, as a reference, should coincide with its focus. The mathematical form is deduced for showing the relation between the deviation of F′ and C and the F-number for a reference transmission sphere. The simulation of calculating the coincidence tolerance between F′ and C is shown with ZEMAX software (Focus Software Inc.). The setup to test the coincidence tolerance is designed with the reference flat in Zygo GPI interferometer. The interferograms have been given to show the coincidence value for three self-developed transmission spheres. All the wavefront errors related to the coincidence tolerance between F′ and C are less than five wavelength. The coincidence tolerance between F′ and C is less than 0.03 mm for F/1.5 transmission sphere, and 5 μm for F/0.75 transmission sphere.