Diffractive optical surfaces with spatially variable structures angle

为了制造紧凑和高功能的光学系统，需要具有复杂结构的技术表面。可实现的复杂程度由制造过程提供的自由度给出。对于衍射光学元件的制造，可用的自由度主要关注光学元件在有限表面积内的高度，通常称为像素。该表面区域内的表面角称为结构角，由制造工艺决定。结构角度在很大程度上决定了元件的光学功能。当前调制结构角度的方法要么局限于简单的几何形状，要么导致制造工作量和近似相关误差的显著增加。目前还没有一种方法可以利用结构角的直接调制来制造复杂的衍射光学器件。这种方法可以产生一类新的光学元件，它可以调制波场的相位和相位梯度，从而结合衍射光学和自由光学的优点。由于这些光学器件的独特特性，可以开发出不受光源时间相干性影响的光束整形系统。例如，这些结构可以用作防伪标签，可以使用移动电话的摄像头进行验证。对于激光材料加工，它们可以用作光束整形光学元件，产生高的重建质量独立于所使用的光源。该项目的目标是为实现和利用金刚石车削过程中空间变化的结构角度提供科学基础。一方面，应开发一种制造工艺，允许在制造过程中动态调整结构角度。另一方面，应开发一个物理模型和设计方法，以显示在这种新的自由度下梁整形的主要和实际边界。为了验证所开发的方法和模型，需要制作一个光学表面，以便在不同的重建距离上形成预定义的强度分布。因此，开发了一种用于实现允许使用普通移动电话验证真伪的防伪系统的基础。

For the fabrication of compact and highly functional optical systems, technical surfaces with a complex structure are required. The degree of attainable complexity is given by the degrees of freedom offered by the fabrication process. For the fabrication of diffractive optics, the available degrees of freedom mostly concern the height of the optical element within a limited surface area, often referred to as pixel. The surface angle within that surface area is termed structure angle and is determined by the fabrication process. The structure angle determines the optical functionality of the element to a high degree. Current Methods for a modulation of the structure angle are either restricted to simple geometries or result in a significant increase of fabrication effort and approximation related errors. There is currently no approach that facilitates the exploitation of a direct modulation of the structure angle for the fabrication of complex diffractive optics.Such an approach could yield a new class of optical elements, that modulate both the phase and the phase gradient of wave fields and thereby combine the advantages of diffractive and freeform optics. Because of the unique properties of these optics, systems could be developed that allow beam shaping independent of the temporal coherence of the light source. These structures could e.g. be used as anti-counterfeiting tags that can be verified using the camera of a mobile phone. For laser material processing, they could be used as beam shaping optics, that yield a high reconstruction quality independent of the utilized light source.The goal of the project is the development of the scientific foundations for the realization and utilization of a spatially varying structure angle in a diamond turning process. On the one hand, a fabrication process shall be developed, that allows for the dynamic adjustment of the structure angle in the fabrication process. On the other hand a physical model and design approach shall be developed, that displays the principal and practical boundaries for beam shaping with this new degree of freedom. For the demonstration of the developed methods and models, an optical surface shall be fabricated, that facilitates the formation of predefined intensity distributions at different reconstruction distances. Thereby, a foundation is developed for the realization of an anti-counterfeiting system that allows verification of authenticity with common mobile phones.