Field-dependent aberrations for misaligned reflective optical systems

Abstract

The performance of optical imaging systems relies on control of aberrations that can arise from limitations in the design, manufacture, or alignment. This dissertation addresses the form of aberrations that occur for misaligned reflective systems, such as telescopes. The relationship between a characteristic set of field-dependent aberrations and the misalignments that cause them is systematically explored. A comprehensive technique that quantifies field performance for a 5-mirror system is given, using Monte Carlo analysis to provide confidence levels of image quality as functions of manufacturing and alignment errors. This analysis is an example of the "forward problem"— determining optical performance of a system if the errors are assumed. The inverse problem — determining the state of alignment based on measurements of performance — is more difficult. The solution to the inverse problem for a multiple mirror system requires an understanding of the complex coupling between many degrees of freedom (tilt, decenter, despace, shape error) of the optical elements and field-dependent aberrations.This work builds on previous treatment of field dependent optical aberrations from Tessieres, Thompson, Shack, Buchroeder and others. A basis set of field-dependent aberrations orthogonal over both field and pupil are developed here and used to describe systems with misaligned and misshapen optics. This description allows complete representation of high order and non-linear effects. The functional form of aberrations that are characteristic of mirror tilt, shift, and deformation show some useful patterns that provide insight to the fundamental effects of misalignment.The use of singular value decomposition to create orthogonal combinations of the field dependent aberrations provides a powerful tool for evaluating a system and for estimating the state of alignment using wavefront measurements. The following optical systems are evaluated to investigate the linear coupling between misalignment and the resulting field dependent aberrations:* 2-mirror telescopes, evaluating well-understood effects for an axisymmetric system and developing the relationships for an unobscured system.* 4-mirror correctors for a spherical primary telescope.The tools and methods are applied to reflective optical systems for astronomical telescopes, but the methods are general and can be useful for any optical imaging system.