A self-calibrating interferometric method for asphere and freeform testing

该项目旨在开发一种灵活的自校准方法，用于非球面和自由曲面的测试。该方法应克服测量的稳定性、精确度和速度方面的现有限制。出发点是倾斜波干涉法。这种方法允许在不改变仪器的情况下测试大量样品。特别地，对旋转对称表面没有限制。测量数据的记录可以在30秒内完成。该方法的一个关键部分是仪器的校准。只要环境条件的变化可以忽略不计，校准结果就是有效的。否则，测量中会出现系统误差，或者需要进行耗时的重新校准。特别是对于接近生产链的应用，需要对环境条件的鲁棒性。自校准方法允许在测量过程中的系统参数的重建产生一个显着减少的校准时间。作为该项目的第一个目标，干涉仪的几何模型的开发。该模型进行了分析，相对于静态和动态参数和不同数量之间的依赖关系的分离。要识别允许根据测量数据进行良好条件重建的一组参数。从这个模型开始，可以构造一种方法，该方法将系统冗余引入测量，并利用这种冗余来进行系统和试样参数的数值重建。关键量是测量结果的横向分辨率。对于单发干涉测量，10微米范围内的分辨率仅在成像光学器件的可变焦平面的情况下是可能的。目前，这会改变系统的状态，需要重新校准。自校准方法允许在测量期间直接重建参数中的诱导变化，而无需在不同位置使用参考对象。这将测量时间从30分钟缩短到1分钟。在这个项目中，该方法在实验室演示实验验证。该项目的一部分是设计具有可变焦平面的成像光学器件，该可变焦平面特别针对其对整个系统的校准状态的影响进行了优化。

This project aims at the development of a flexible and self-calibrating method for the testing of aspheres and freeforms. The method should overcome existing limitations concerning stability, precision and speed of the measurement. Starting point is the Tilted-Wave-Interferometry. This method allows testing a large class of specimen without changes in the instrument. In particular, there is no limitation to rotationally symmetric surfaces. The recording of the measurement data can be performed in less than 30 seconds. A crucial part of the method is the calibration of the instrument. The calibration result is valid, as long as the environmental conditions change only negligibly. Otherwise, either a systematic error in the measurement occurs or a time-consuming re-calibration is necessary. In particular with respect to applications close to the production chain, robustness against environmental conditions is desirable. A self-calibrating method allows the reconstruction of the system parameters during measurement yielding a significantly reduced time for calibration.As a first aim of the project, a geometrical model of the interferometer is developed. This model is analyzed with respect to separation of static and dynamic parameters and dependencies between different quantities. A set of parameters which allows a well-conditioned reconstruction from measurement data is to be identified. Starting from this model, a method can be constructed which introduces systematic redundancies to the measurement and exploits this redundancies for a numerical reconstruction of system as well as specimen parameters. A critical quantity is the lateral resolution of the measurement result. For a single-shot interferometric measurement, a resolution in the range of 10 microns is only possible with a variable focal plane of the imaging optics. Currently, this changes the state of a system and requires a re-calibration. The self-calibrating method allows reconstructing the induced change in the parameters directly during the measurement, without the use of a reference object in different positions. This reduces the measurement time from 30 minutes to 1 minute. In this project, the method is experimentally validated at a lab demonstrator. One part of the project is the design of an imaging optics with a variable focal plane which is optimized in particular with respect to its influence on the calibration state of the complete system.