Kim Goeun, Song In-Ung, Gyu Park June, Kihm Hagyong, Yang Ho-Soon
Appl Opt. 2020 Oct 1;59(28):8681-8687. doi: 10.1364/AO.402543.
The Ritchey-Common test is a widely used method for testing flat mirrors with a larger reference spherical mirror. However, with the increase in the size of the flat mirror, the fabrication of the spherical mirror becomes more time consuming and expensive. In this study, we developed a novel technique to test a large flat mirror with a smaller reference sphere using a dual subaperture stitching (DSS) method. One part of the DSS technique is a modified Ritchey-Common test, which uses a reference sphere smaller than the flat mirror. The other part involves scanning along the centerline of the flat mirror. The former can be used to determine the surface form error (SFE), except for rotationally symmetric components, such as power and spherical aberrations, which can be measured by the latter. To perform the stitching process using a smaller reference sphere, the flat mirror was repeatedly rotated by a fixed angular step. One of the advantages of the rotation of the flat mirror is that it can be used to identify the errors resulting from the reference sphere, which do not vary during the rotation of the flat mirror. We verified the DSS method using a 152 mm diameter optical flat mirror and determined the root-mean-square (rms) measurement error to be only 0.2 nm, which was comparable to the error of the full-aperture interferometric measurement. In addition, we tested a 1.2 m diameter flat mirror with a reference sphere with an aperture of 0.8 m and measured its SFE to be 11.9±0.5 rms.
里奇-康芒测试是一种广泛用于用较大参考球面镜测试平面镜的方法。然而，随着平面镜尺寸的增加，球面镜的制造变得更加耗时且昂贵。在本研究中，我们开发了一种新技术，使用双子孔径拼接（DSS）方法用较小的参考球体测试大尺寸平面镜。DSS技术的一部分是一种改进的里奇-康芒测试，它使用比平面镜小的参考球体。另一部分涉及沿平面镜中心线进行扫描。前者可用于确定除旋转对称分量（如光焦度和球差）之外的表面形状误差（SFE），后者可测量这些旋转对称分量。为了使用较小的参考球体执行拼接过程，平面镜以固定的角步长反复旋转。平面镜旋转的优点之一是它可用于识别由参考球体引起的误差，这些误差在平面镜旋转过程中不会变化。我们使用直径为152毫米的光学平面镜验证了DSS方法，并确定均方根（rms）测量误差仅为0.2纳米，这与全孔径干涉测量的误差相当。此外，我们用孔径为0.8米的参考球体测试了直径为1.2米的平面镜，并测量其SFE为11.9±0.5 rms。
