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

在光学工业中，自由曲面的光学测量是质量保证过程的强制性前提。高性价比、高精度的非球面面形测量仍然是一项具有挑战性和悬而未决的任务。因此，在第一个资助期内，研究了剪切干涉测量对非球面和自由形状检测的限制和机会。剪切干涉测量的最大好处是它允许同时使用多个独立的光源作为照明。这使得即使干涉仪成像系统的接受角有限，也可以研究具有陡峭坡度的大样本。因此，剪切照相方法结合了几何光学方法的典型的大照明孔径，例如偏转法，以及干涉测量所提供的高精度。第一个资助期的一个重要成果是一种全新的测量自由曲面的方法，该方法基于相互相干的获取，被称为多孔径剪切干涉测量(MARS)。验证火星科学和技术基础所需的所有实验都是在透明物体通过照明光线传输的情况下进行的。然而，对于工业应用，反射方向的测量是强制性的。在对火星接近的研究中，很明显，在反射配置下的测量比最初预期的更具挑战性。照明的一部分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，在没有样品的情况下，光源的位置不能通过简单的校准测量来确定，这对评估过程至关重要。最后，如果样品是由玻璃制成的，会产生两个反射，一个从正面，一个从反面。因此，科技问题使得在第一个资助期的框架内发展反思模式显得不切实际。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，以实现反思模式的配置。目前的结果表明，火星有可能引发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一潜力。

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.