Monolithic Three-Mirror Anastigmat Telescope

Abstract

This thesis presents the design of a near-infrared (near-IR) three-mirror anastigmat telescope with a focal length of 38,675.1 ??, an entrance pupil diameter of 1,933.75 ??, and a 0.12° full field-of-view (FoV). This diffraction-limited telescope has a RMS spot radius of 36.6 μm (similar to the radius of Airy disk) to satisfy the design resolution requirements of the IR telescope. Designed specifically for near-IR sensing, the system benchmarked a widely known module of an IR detector, called the Near-Infrared Camera (NIRCam) detector, with ten Teledyne HgCdTe H2RG detectors. The NIRCam detector was assumed in this TMA design study, similar to the James Webb Space Telescope case. This three-mirror telescope design contains only two substrates, one consisting of two mirror surfaces with different radii of curvature. Consequently, the structure of this robust telescope design is straightforward and it is therefore easy to manufacture and align. The starting point for the optical design of this telescope was the Vera C. Rubin Observatory (a.k.a. Large Synoptic Survey Telescope), a three-mirror anastigmat system combined with more refractive lenses and a color filters. Importantly, the specifications of these three mirrors were changed to achieve the goal of aberration balancing. To determine the tolerances of the optical design, the M2 mirror substrate was misaligned with respect to the M1/M3 monolithic mirror, and the realistic maximum error was evaluated. As a result, in the range of 36.6 ?? root mean square (RMS) spot radius for the three degrees of freedom (DoF), the calculated tolerances were 0.0072° for X-rotation, 43 µ? for Y-translation, and 7.6 µ? for Z-translation. This result confirmed that the required machining accuracy to build the proposed telescope is within the advanced optical fabrication (e.g., diamond turning) and modern integration capabilities.