基于双回转相位板的非球面子孔径测量技术

Subaperture Testing Technique of Aspheres Based on Counter-Rotating Phase Plates

子孔径拼接技术与补偿检验技术的结合能够增加干涉仪的横向和垂直动态测量范围,适用于大口径、大非球面度的非球面的面形测量。利用一对相向回转的Zernike相位板作为近零位补偿器,产生可变的像差,补偿不同非球面在不同离轴位置的子孔径像差,使其剩余像差减小到干涉仪的垂直动态测量范围内。通过计算两个待测非球面的子孔径像差,求解Zernike相位板的相位函数;同时结合四台阶刻蚀工艺和载频技术,成倍提高衍射效率并隔离干扰衍射级次的影响。以同温层红外线天文台(SOFIA)望远镜的凸双曲面次镜和凹非球面反射镜为例,验证了该近零位补偿器实现不同非球面的子孔径像差补偿的能力,表明其具有良好的面形适应性。

Subaperture stitching interferometry in combination with null test can extend the lateral and vertical dynamic range of measurement, which is applicable to surface figure measurement for large aperture and high-departure aspheres. By employing a pair of counter-rotating Zernike phase plates as near-null optics, variable aberration is generated to balance most of the aberration for subapertures at different locations on various aspheric surfaces. The residual aberration is hence reduced within the vertical dynamic measurement range of a standard interferometer. The subaperture aberration of two test aspheres is calculated to solve the phase function of the Zernike plates. Meanwhile, the four-step etching process and power carrier are introduced to double the efficiency of diffraction and isolate the disturbance orders of diffraction. Finally the flexibility of the near-null optics is well demonstrated by applying it to the convex hyperbolic secondary mirror of stratospheric observatory for the infrared astronomy （SOFIA） telescope and a concave asphere. All subaperture aberrations are successfully reduced by the near-null optics, which shows its good adaptability to surface shape.