A Lap-MRF process is proposed for large aperture mirrors. In Lap-MRF, a lap is used to expand the polishing area, which improves the material removal rate. Moreover, the MR fluid can be renewed continuously to ensure the stability of the material removal rate, which improves the convergence efficiency of the surface profile error. In this paper, the figuring ability of the Lap-MRF removal function is analyzed. The Lap-MRF process, which is based on surface profile filtering, is presented. Finally, a series of figuring experiments on a Φ350 mm K9 mirror are carried out. For the Lap-MRF removal function, the volume removal rate is up to 0.48 mm³ /min and the cut-off frequency is about 0.03 mm^-1 . After four times figuring using Lap-MRF, the surface profile error throughout the whole surface is improved to 4.84 λ (λ= 632.8 nm) PV (Peak-to-Valley), 0.69 λ RMS (Root Mean Square) from 25.24 λ PV, 4.31 λ RMS and its total convergence ratio of the RMS error is up to 6.32. These results verify the validity of the proposed method for large aperture mirrors.

Date Published: 18 December 2019
PDF: 8 pages
Proc. SPIE 11341, AOPC 2019: Space Optics, Telescopes, and Instrumentation, 113411S (18 December 2019); doi: 10.1117/12.2547745

Published in SPIE Proceedings Vol. 11341:
AOPC 2019: Space Optics, Telescopes, and Instrumentation
Suijian Xue; Xuejun Zhang; Carl Anthony Nardell; Ziyang Zhang, Editor(s)