Rapid fabrication of lightweight SiC aspheres using reactive atom plasma (RAP~TM) processing

摘要

Polishing has traditionally been a process of mechanical abrasion with each iteration removing the damage from the previous iteration. Modern sub-aperture techniques such as CCOS, MRF polishing etc. have added a considerable amount of determinism to this iterative approach. However, such approaches suffer from one significant flaw, I.e., the algorithms are completely guided by figure error. This approach fails when there is a considerable amount of strain energy stored in the substrate and becomes very evident when the aspect ratio of the mirror increases significantly causing relaxation of strain energy to have deleterious and unpredictable effects on figure between iterations. This is particularly pronounced when the substrate is made of a hard ceramic such as silicon carbide requiring a considerable amount of pressure to obtain any appreciable material removal rate. This paper presents an alternate approach involving a stress-free figuring step and a buffing step intended to recover the surface roughness.