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.

为了精确确定光学表面的质量，可以使用干涉测量方法。该设置通常被排列为无效测试，其中仅测量样品与其理想表面形状的偏差。波前与表面的必要匹配是由所谓的空镜头完成的。对于非球面，衍射光学元件（DOE）是合适的。由于光刻生产的灵活性，结构可以轻松地调整为各种表面形状，而光刻过程的精度以及使用高质量的平面表面，可确保能够高质量。由于所需的少量时间，在测试具有高数值孔径（NA）的样品时有限。此外，抛光后只能测试表面，因为粗糙表面上的相干照明会导致斑点噪声，从而损害了测量值。众所周知的几何形状以任意孔径测试粗糙的物体是放牧的入射率。为了适应此过程，以测试高光圈，甚至可能是粗糙的无球表面，在此提议通过DOE将波正面调整为沿沥青的子午线曲线的特定切线平面。对于球体/沥青，这会导致子午线曲线周围的小区域进行局部无效测试。因此在反射和传播中测量的优势。确定表面偏差（如在反射中），但没有任何干扰的背部反射（如传输中）。由于放牧的发生率，波长增加到有效波长，与照明波长相比，该波长通常要大得多。因此，可以在抛光之前测量技术表面。此外，可以从任何视角（除了一个小轴承区域除外）测量测试样品，以便可以测试具有高数值的对象。凸，粗糙（包括光滑），旋转对称的间谍应根据衍射放牧的入射干涉仪开发。所述方法可以测量旋转对称的粗糙表面，并在子微米计方案中具有粗糙度。这甚至在最终抛光过程之前就会导致光学表面的表征。