A simulation and experimental validation of third-order coma in nodal aberration theory with a Cassegrain telescope

Authors: ÖZGÜR KARCI

Abstract: This study presents a simulation and experimental validation of third-order coma in Nodal Aberration Theory (NAT) with a custom-designed Cassegrain system. The Cassegrain system uses a piezo-driven flexure tool to align the telescope's secondary mirror with respect to the primary mirror. This alignment mechanism is also used to misalign the telescope's secondary mirror to induce the intentional aberrations. The third-order Fringe Zernike coma (Z$_{7/8}$) was simulated utilizing the Cassegrain telescope's real ray-trace model (e.g., in Code V) and analyzed for both the telescope's nominal aligned and misaligned states. The simulated aberration of third-order coma was induced utilizing the secondary mirror misalignments and measured interferometrically on a $5\times 5 $ mesh of field points on the telescope's focal plane. The experimental results were compared with simulation results, and we showed that the results are consistent with each other. Hence, we validated the shift of aberration field center (zero coma, or coma node) from the optical axis, where the third-order coma is linear with the field as predicted by NAT for the Cassegrain telescope. For demonstrating the stability and accuracy of the experimental results, a statistical analysis was conducted.

Keywords: Nodal Aberration Theory, Cassegrain telescope, third-order coma, telescope alignment, spaceborne telescopes, optical imaging systems

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