Interferometric testing of aspheres using gracing incidence

使用掠射入射对非球面进行干涉测量

• 批准号: 397020295
• 负责人: Professor Dr. Norbert Lindlein
• 金额: --
• 依托单位: Max-Planck-Institut für die Physik des Lichts
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/397020295?language=en
• 关键词: Interferometric; testing; aspheres; using; gracing

For the precise determination of the quality of optical surfaces, interferometric measurement methods can be used. The setup often is arranged as a null test, where only deviations of the specimen from its ideal surface shape are measured. The necessary matching of the wave front to the surface is done by so called null lenses. For aspheric surfaces, diffractive optical elements (DOE) are suitable. Due to the flexibility of the lithographic production, the structures can easily be adjusted to various surface shapes, while the precision of the lithographic process, together with the use of high quality planar surfaces, ensures a high quality of the DOE.However, DOEs are limited when testing samples with high numerical aperture (NA), due to the required small periods. Furthermore, the surfaces only can be tested after polishing, because coherent illumination on rough surfaces leads to speckle noise, impairing the measurements.A well known geometry to test rough objects with arbitrary aperture is grazing incidence interferometry. To adapt this procedure for the testing of high aperture, and maybe rough aspheric surfaces, it is proposed here to adapt the wave front via DOE to the particular tangent plane along the meridian curve of the asphere. For spheres/aspheres this leads to a local null test in a small area around the meridian curve. The region under test on the asphere is therefore limited to a small neighbourhood of the meridional curve, nevertheless by rotation of the test sample around the axis of symmetry the whole surface can be measured.The unique properties of the grazing incidence geometry leads to a combination of the advantages of measurements in reflection and transmission. The surface deviations are determined (as in reflection) but without any disturbing back reflections (as in transmission). Due to the grazing incidence, the wavelength is increased to an effective wavelength, which, in general, is much greater compared to the illumination wavelength. Therefore it is possible to measure technical surfaces before polishing. In addition, the test sample can be measured from any angle of view (besides a small bearing area), so that objects with high numerical aperture can be tested.In this project, a method for the high-precision measurement of the meridian curve of convex, rough (incl. smooth), rotationally symmetric aspheres shall be developed based on a diffractive grazing incidence interferometer. The described method enables the measurement of rotationally symmetric, rough surfaces with roughnesses in the sub-micrometer regime. This leads to a characterisation of optical surfaces even before the final polishing process.

为了精确测定光学表面的质量，可以使用干涉测量方法。该设置通常被安排为零测试，其中仅测量样本与其理想表面形状的偏差。波前与表面的必要匹配是通过所谓的零透镜来完成的。对于非球面表面，衍射光学元件 (DOE) 是合适的。由于光刻生产的灵活性，结构可以很容易地调整为各种表面形状，而光刻工艺的精度以及高质量平面的使用确保了 DOE 的高质量。然而，由于所需的周期较小，在测试高数值孔径 (NA) 样品时 DOE 受到限制。此外，表面只能在抛光后进行测试，因为粗糙表面上的相干照明会导致散斑噪声，从而损害测量。用于测试具有任意孔径的粗糙物体的众所周知的几何结构是掠入射干涉测量法。为了使该程序适应大孔径以及可能粗糙的非球面表面的测试，这里建议通过DOE使波前适应沿着非球面的子午曲线的特定切平面。对于球面/非球面，这会导致在子午曲线周围的小区域内进行局部零测试。因此，非球面上的测试区域仅限于子午曲线的一个小邻域，但通过测试样品绕对称轴旋转，可以测量整个表面。掠入射几何形状的独特特性导致反射和透射测量优点的结合。表面偏差被确定（如在反射中），但没有任何干扰的背反射（如在透射中）。由于掠入射，波长增加到有效波长，该有效波长通常比照明波长大得多。因此，可以在抛光之前测量技术表面。另外，测试样品可以从任何视角（除了小承载面积）进行测量，从而可以测试高数值孔径的物体。本项目将开发一种基于衍射掠入射干涉仪的凸面、粗糙（包括光滑）、旋转对称非球面球面子午线高精度测量方法。所描述的方法能够测量粗糙度在亚微米范围内的旋转对称的粗糙表面。这甚至可以在最终抛光过程之前对光学表面进行表征。