Design and Fabrication of freeform mirrors for the KASI-Deep Rolling Imaging Fast Telescope

We fabricated three freeform mirrors for the KASI-Deep Rolling Imaging Fast Telescope, which is a confocal off-axis freeform three-mirror system with a 300 mm entrance pupil diameter. We applied lightweight design and analysis to minimize weight while preserving the performance of the system. As a result, the weight of the primary and tertiary mirrors was reduced by 72.4% and 74.2%, respectively. Additionally, the wavefront analysis yielded RMS surface error less than 20 nm. The surfaces of these off-axis freeform mirrors were formed by a series of production process, including grinding, polishing, forming, and finishing. Measuring surface profile has been performed by using Coordinate Measuring Machines (CMMs) for the grinding process and an interferometer with Computer Generated Holograms (CGHs) for polishing, forming, and finishing process. The test results for all three mirrors were well within the required value of 20 nm RMS and 100 nm PV.