SiC mirrors are of excellent mechanical and thermal properties compared to their glass opponents. Efficient fabrication and testing of SiC mirrors, particularly the large freeform surfaces are very challenging. In this paper, direct CNC generation, deterministic polishing techniques including CCOS, MRF, and IBF were addressed in detail. Since testing is critical to make high accuracy freeform surfaces, the paper focused on Computer Generated Hologram (CGH) design and implement to measure large mirrors. In particular, detector to mirror mapping distortion was discussed in detail. Finally, some results for SiC mirrors were presented.
In this paper, the influence on the image quality of manufacturing residual errors was studied. By analyzing the statistical distribution characteristics of the residual errors and their effects on PSF and MTF, we divided those errors into low, middle and high frequency domains using the unit “cycles per aperture”. Two types of mid-frequency errors, algorithm intrinsic and tool path induced were analyzed. Control methods in current deterministic polishing process, such as MRF or IBF were presented.
Freeform surfaces provide more design freedoms to imaging system without introducing new types of aberrations,
therefore better performance can be expected. In this paper, the design of a four-mirror telescope with freeform surfaces
was introduced and issues such as tolerancing , manufacturability were discussed; Based on that, fabrication and testing
of freeform surfaces were discussed; Particularly direct CNC generation, deterministic polishing techniques including
CCOS, MRF and IBF Polishing were presented in detail. Since testing is critical to make high accurate freeform surfaces,
the paper focused on Computer Generated Hologram (CGH) design and implement to measure large freeform mirrors. In
particular, correction of detector to mirror mapping distortion was discussed in detail. Finally, the full field alignment
results were given to show the feasibility of using large freeform surfaces in space optics.
Off-axis three-mirror anastigmatic (TMA) system adopt off-axis aspheric mirror for high resolution telescope. However,
residual tooling marks from advanced aspheric fabrication techniques such as computer controlled optical surfacing
(CCOS) are difficult to remove. These marks typically in the mid-spatial frequency (MSF), in optical fabrication also
named surface band error. MSF will reduce MTF and contrast. This paper using Fourier method to research the
relationship between MSF and the reduction, and applies simulation method to analyze the effect of fabrication residual
marks on the loss of MTF in off-axis TMA optical system, also analyze the scatter influence of MSF by plot the
relationship between surface errors PV/RMS and spot diameter.