Fabrication of flat and supersmooth surfaces with bowl-feed polishing process

Abstract

Low-scatter supersmooth optical components are wildly used for critical applications such as high power laser systems, mirrors for ring laser gyros, and low-scatter windows. In this paper, a bowl-feed polishing process with fine abrasives to get flat and extremely smooth surfaces is presented. We consider the machining of super-smooth surfaces as a chain consisted of some key nodes, not merely a polishing process. So after the samples of fused silica have been grinded, fine grinded and lapping previously, each step is controlled strictly, a bowl-feed polishing process is adopted to produce the supersmooth surfaces. During the whole polishing process, in order to achieve consistently reliable and meaningful values of both roughness and flatness, every effort is made to get the proper polishing parameters. Abrasives with different grain size distribution and the temperature are taken into account particularly. Two characters of the samples, roughness and flatness, are concerned about in this study. Process controlling by interferometer implies that surface shape is maintained to better than λ/15 RMS (λ=632.8nm), 100 mm in diameter for an extended periods of time, of the order of days. The surface roughness is tested by an interference microscopy. In best cases, the final test result of surface roughness is better than 0.8nm RMS.

Super-polishing of Zerodur aspheres by means of conventional polishing technology

“…More traditional approach to get angstroem level roughness is to use Teflon polisher and standard polishing slurry 9,10 -as for float polishing it was used for flat samples only. Very interesting is bowl-feed polishing 11,12,13 in which the polishing pad and sample are submerged in polishing slurry and standard pitch tools are used -see Figure1. Many groups involved semiflexible subaperture tools that could be employed in aspheric production together with standard polishing slurries 14,15,16 .…”

Calculation and simulation of the uniformity of grinding removal in ring polishing

“…In particular, optical elements, over a wide size range lying from a few millimeters to hundreds of millimeters, are needed in the ultra-precision optical systems as represented by high power laser systems and ring laser gyros [4] . The surface figure and roughness are also required strictly.…”