Ufuk Ceyhan

• Aspherical lenses are widely used in different applications of modern high quality optics, due to their good optical performance and their potential to reduce the weight and size of the optical systems. Substantial progress in the production technologies of aspherical lenses in the last decade increases the demand on accurate and reliable measurement systems for aspherical surfaces. So far, different measurement methods such as interferometry, Shack-Hartmann wavefront sensors and tactile surface profiling have been proposed. However, because of the complex surface profiles of the aspherical lenses, these methods have significant limitations concerning dynamic range and flexibility. The goal of non-contact measurement of the surfaces of the aspherical lenses without a reference object (null lens or computer generated holograms) is still not achieved. In this thesis, the potential and the limitations of the “experimental ray tracing” (ERT) method for characterization of aspherical lenses are investigated. A new approach called “aspherical surface retrieval” (ASR) based on the ERT method is proposed. This approach allows retrieval of the aspherical surface profile of the lens from the measured slopes of the transmitted rays. In addition, simultaneous measurement of the optical performance of aspherical lenses and the aspherical surface profiles within a single test unit is targeted. Throughout the thesis work, an ERT setup is realized and a software is developed for complete automation of the setup and analysis of the measurement data. The wavefront aberrations are determined using zonal and modal wavefront reconstruction methods. The coefficients of the Zernike polynomials that are fitted to the measurement data are used to determine the focal length. In the ASR approach, the relationship between the slopes of the transmitted rays and the aspherical surface profile is derived. Furthermore, a numerical ray tracing algorithm is written for comparison of the actual and the model aspherical lens. An optimization process minimizing the difference between the actual and the model aspherical lens is used to retrieve the aspherical surface profile. Moreover, the proof-of-principle of the ASR approach is demonstrated using simulations. A Mach-Zehnder interferometer and a Shack-Hartmann wavefront sensor measurement setup is realized for the comparison of the measurements of wavefront aberrations of commercial aspherical lenses with the ERT setup. The measurement results using the ASR approach are verified by the measurements of different aspherical lenses by a commercial tactile surface profiler. The proposed approach based on the ERT method allowed simultaneous measurements of the optical performance and the aspherical surface profile of the lenses.