Optical surface metrology with spatially and temporally partially coherent light wave fields (OPaL 2)

在光学工业中，自由曲面的光学计量是保证质量的必要前提。低成本、高精度的非球面形状测量仍然是一个具有挑战性和未解决的问题。因此，在第一个资助期内，剪切干涉测量法对非球面和自由形状测试的限制和机会进行了研究。剪切干涉测量的最大好处是它允许同时使用多个独立光源作为照明。这使得调查大标本与陡峭的斜坡，尽管有限的接受角度的干涉仪成像系统。因此，剪切成像方法结合了大的照明孔径，这是典型的几何光学方法，如偏转法，与干涉测量提供的高精度。第一个资助期的一个重要成果是一种基于相互相干性获取的测量自由曲面的全新方法，即多孔径剪切干涉测量法（MArS）。所有验证火星科学和技术基础的必要实验都是通过照明光透射透明物体进行的。然而，对于工业应用，反射方向的测量是强制性的。在对火星的研究过程中，很明显，在反射配置中的测量比最初预期的要具有挑战性得多。一部分照明必须来自干涉仪成像孔径的方向，这意味着光源必须位于成像路径内。此外，光源的位置，这是必不可少的评估过程，不能通过一个简单的校准测量没有标本确定。最后，如果样品是由玻璃制成的，则会产生两个反射，一个来自正面，一个来自反面。因此，科学和技术问题使得在第一个资助期框架内建立一个反思模式显得不现实。因此，第二个资助期的目标是通过应对上述挑战，进一步发展MArS方法，使其朝着反射模式配置。目前手头的结果表明，MArS有可能启动非球面透镜光学计量学的范式转变。现在的目标必须是提高这种潜力。

Optical metrology of free form surfaces is a mandatory prerequisite for the process of quality assurance in the optical industry. Cost efficient and precise form measurement of aspheric surfaces is still a challenging and unsolved task. Therefore, within the first funding period, the limits and opportunities offered by shear interferometry towards aspheric and free form testing have been investigated. The great benefit of shear interferometry is that it allows for using multiple independent light sources as illumination at the same time. This enables the investigation of large specimen with steep slopes despite the limited acceptance angle of the interferometers imaging system. Hence, the shearographic approach combines a large illumination aperture, which is typical to geometric optical methods, such as deflectometry, with the high precision offered by interferometry. An important result of the first funding period is an entirely novel approach to measure free form surfaces based on the acquisition of the mutual coherence, which was coined Multi Aperture Shear Interferometry (MArS). All experiments necessary to validate the scientific and technical foundation of MArS were conducted with transparent objects being transmitted by the illuminating light. However, for industrial applications, measurements in reflection direction are mandatory. During the research on the approach of MArS it became clear that the measurement in reflection configuration is far more challenging than initially anticipated. A part of the illumination has to come from the direction of the imaging aperture of the interferometer, which means that light sources have to be positioned within the imaging path. Additionally, the positions of the light sources, which are essential to the evaluation process, cannot be determined by a simple calibration measurement without specimen. Finally, if the specimen is made from glass, two reflections arise, one from the front side and one from the reverse side. As a consequence, the scientific and technical problems let the development of a reflection mode setup within the frame of the first funding period appear unrealistic. Therefore, the aim of the second funding period is to further develop the MArS approach towards a configuration in reflection mode, by tackling the above challenges. The current results at hand indicate that MArS has the potential to initiate a paradigm shift in optical metrology of aspheric lenses. The objective now must be to raise this potential.