Advanced studies on the measurement of aspheres and freeform surfaces with the tilted-wave interferometer

Abstract

This work presents further insight into the working principles of the tilted-wave interferometer regarding the system characterization for the measurement of aspheres and freeform surfaces. A method to characterize an optical system for the measurement of aspheric and freeform surfaces without dedicated null optics in a non-null measurement fashion is presented. Even though non-null test arrangements allow for increased measurement flexibility the evaluation of the measurement results becomes much more complex than in the null test variant. The problem becomes then the identification of small phase deviations caused by the test surface in the presence of systematic system aberrations several orders of magnitude larger. The characterization of the interferometer aberrations plays hereby a central role in the measurement process for an accurate assessment of the test surface. In this work, a novel method for the characterization of the interferometer setup is described and measurement results in a non-null test configuration for an aspheric element with several hundred waves departure from its best-fit sphere presented.