Subaperture approaches for asphere polishing and metrology

Abstract

This paper summarizes some of QED Technologies' latest developments in the fi eld of high-precision polishing and metrology.Magneto-Rheological Finishing (MRF) is a deterministic sub-aperture polishing process that overcomes many of the fundamental limitations of traditional fi nishing. MRF has demonstrated the ability to produce optical surfaces with accuracies better than 30 nm peak-to-valley (PV) and surface micro-roughness less than 0.5 nm rms on a wide variety of optical glasses, single crystals, and glass-ceramics. The MR fl uid forms a polishing tool that is perfectly conformal and therefore can polish a variety of shapes, including fl ats, spheres, aspheres, prisms, and cylinders, with either round or rectangular apertures.QED's Sub-aperture Stitching Interferometer (SSI) complements MRF by extending the effective aperture, accuracy, resolution, and dynamic range of a phase-shifting interferometer. This workstation performs automated sub-aperture stitching measurements of spheres, fl ats, and mild aspheres. It combines a six-axis precision stage system, a commercial Fizeau interferometer, and specially developed software that automates measurement design, data acquisition, and the reconstruction of the full-aperture map of fi gure error. Aside from the correction of sub-aperture placement errors (such as tilts, optical power, and registration effects), our software also accounts for reference-wave error, distortion, and other aberrations in the interferometer's imaging optics. By addressing these matters up front, we avoid limitations encountered in earlier stitching work and signifi cantly boost reproducibility beyond that of the integrated interferometer on its own.

Sub aperture polishing of Fused Silica asphere for deterministic control of form and texture

“…In sub aperture polishing, the tool and polishing medium selection is driven by the localized radius of asphere as well as the material properties. We used polyurethane (LP66) and Uninap cloth for various polishing cycles [6].…”

Design of an holographic off-axis calibration light source for ARGOS at the LBT

“…We achieve excellent thermal stability by using Clearceram as material for the lens with the ellipsoidal surface. Coputer numerical controlled (CNC) grinding and polishing, followed by subsequent magnetorheological finishing (MRF) yields a surface accuracy of approximately λ/10 peak to valley [5].…”

Subaperture stitching interferometry based on digital holography

“…This workstation is capable of extending the effective aperture, accuracy, resolution, and dynamic range of a standard interferometer, and can automatically carry out high quality subaperture stitching of flat, spherical, and aspherical surfaces. It combined a six-axis precision stage system, a commercial Fizeau interferometer, and specially developed software to orchestrate measurement design, motion control, data acquisition, reconstruction of the full-aperture map [5][6][7][8]. CSIRO's Australian Centre for Precision Optics has devised and built a subaperture stitching interferometer for production of a high precision, high numerical aperture spherical mirror.…”