Absolute test technology for rotation and translation interference based on lightweight calibration mirror
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摘要: 光学干涉绝对检验技术能够实现参考面和待测面面形的有效分离，是对干涉仪进行精度标定的有效手段。面向大口径平面干涉仪的校准需求，旋转平移法仅需一块透射平晶和一块反射平晶，避免了额外加工第3块平晶的成本和难度。但随着口径的增大，自重和支撑使得反射平晶在平移和旋转多种状态下的变形较大，继而影响绝对检验精度。提出设计轻量化的校准反射镜作为反射平晶，采用旋转平移法实现大口径干涉仪的绝对检验。以Φ 1 500 mm平面干涉仪作为标定需求，采用碳化硅作为校准反射镜材料，以三角形轻量化结构和6点背部支撑方式进行轻量化设计，控制其质量仅为93 kg，支撑和重力引入的面形变形PV值为9.75 nm。将变形面形叠加至PV值λ/4、不同分布的加工面形进行旋转平移绝对检验仿真计算，对旋转对称程度低且包含较多高频成分的面形，检验精度为λ/30；而对分布平滑对称的面形，检验精度可达到λ/50。因此，为了实现对于大口径平面干涉仪λ/50精度的标定目标，要求碳化硅校准反射镜加工面形PV值低于λ/4,尽量避免高频成分,旋转对称程度高。Abstract: The optical interference absolute test technology can separate the surface figures of the reference plane as well as the tested optics, and it is an effective means to calibrate the accuracy of the interferometer. For the calibration requirements of large-aperture plane interferometer, the rotation translation method only requires one transmission flat and one reflective flat, which avoids the cost and difficulty of processing an additional flat. However, with the increase of the caliber, the weight and support make the deformation of the reflective flat larger in various states of translation and rotation, and then affect the absolute test accuracy. Therefore, it was proposed to design a lightweight calibration mirror as a reflective flat, and used the rotation translation method to realize the absolute test of the large-aperture interferometer. The Φ 1 500 mm plane interferometer was used as the test requirement, the SiC was used as the calibration mirror material, and the lightweight design was carried out with a triangular lightweight structure and a six-point back support method. The weight was controlled to only 93 kg, and the surface deformation PV value introduced by the support and gravity was 9.75 nm. It superimposed this deformed surface shape to PV value of λ/4, and performed rotation translation absolute test simulation calculation for processing surface shapes of different distributions. For the surface shapes with low degree of rotational symmetry and containing more high-frequency components, the test accuracy is λ/30, and for the smooth and symmetrical surface shapes, the test accuracy can reach to λ/50. Therefore, in order to achieve the λ/50 accuracy calibration target for the large-aperture plane interferometer, it requires that the PV value of the processed surface of the SiC calibration mirror is lower than λ/4, try to avoid high-frequency components, and have a high degree of rotational symmetry.
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图 5 3种典型面形及其中高频信息
Fig. 5 Three typical surface shapes and medium-high frequency information
图 6 不引入支撑和重力作用变形的旋转平移法仿真
Fig. 6 Simulation of rotation and translation method without support and gravity deformation
图 7 引入支撑和重力作用变形的旋转平移法仿真
Fig. 7 Simulation of rotation and translation method with support and gravity deformation
表 1 轻量化网格理论分析对比
Table 1 Comparison of lightweight grid theory analysis
三角形 六边形 圆形 单个网格空心面积$A$ $\dfrac{{\sqrt 3 }}{4}{D^2}$ $\dfrac{{\sqrt 3 }}{2}{D^2}$ $\dfrac{\pi }{4}{D^2}$ 空间栅格面积$S$ $ \dfrac{3\sqrt{3}}{2}(1+\alpha {)}^{2}{D}^{2} $ $\dfrac{{\sqrt 3 }}{4}{(1 + \alpha )^2}{D^2}$ $\dfrac{{\sqrt 3 }}{4}{(1 + \alpha )^2}{D^2}$ 筋的面积${S_{{R} } }$ $ \dfrac{3\sqrt{3}}{2}(1+\alpha {)}^{2}{D}^{2} $ $\dfrac{{\sqrt 3 }}{2}\alpha {D^2} + \dfrac{{\sqrt 3 }}{4}{\alpha ^2}{D^2}$ $\dfrac{{\sqrt 3 }}{4}{(1 + \alpha )^2}{D^2} - \dfrac{\pi }{8}{D^2}$ 筋的分布率$R$ $1 - \dfrac{1}{{{{(1 + \alpha )}^2}}}$ $1 - \dfrac{1}{{{{(1 + \alpha )}^2}}}$ $1 - \dfrac{\pi }{{2\sqrt 3 }}\dfrac{1}{{{{(1 + \alpha )}^2}}}$ 
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