Magnetorheological finishing of edges of optical elements

Abstract

Method and apparatus using magnetorheological fluid for finishing a non-image-forming edge of an optical element to a very high degree of smoothness and for removing microscopic fissures from such edges, the method comprising positioning an optical element near a continuous carrier surface such that a converging gap is defined between an edge of the optical element and the carrier surface, the element being disposed such that image-forming refractive and reflective surfaces thereof do not create a gap with the carrier surface; applying a magnetic field substantially at the gap; introducing a magnetorheological fluid onto the carrier surface; driving the magnetorheological fluid through the gap to cause a flow of magnetic field-stiffened magnetorheological fluid through this gap to create a work zone and to form a transient finishing tool for removing material from the edge of the optical element; and moving the optical element relative to the work zone to expose different portions of the edge to the fluid for predetermined time periods to finish the edge to a predetermined degree. The lateral extent of fluid may be broad enough to permit polishing of a plurality of optical elements simultaneously on a single carrier surface, or a plurality of finishing stations may be ganged to finish a plurality of optical elements on a plurality of carrier surfaces.