25 September 2008 Metal mirrors with excellent figure and roughness
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Abstract
An outstanding technique in point of ultra-precision as well as economical production of mirrors is Single Point Diamond Turning (SPDT). The unique properties of the diamonds are used to get optical surfaces with roughness values down to 5 nm rms (root mean square) and very precise form accuracy down to 70 nm rms and 500 nm p.-v. (peak to valley) value over an area of 200 mm x 200 mm. This quality level is typical for applications in the Near Infrared (NIR) and Infrared (IR) range. For applications in the VIS and UV range the turning structures must be removed with a smoothing procedure in order to minimize the scatter losses. Favorable is an aluminium base body plated with a thick-film of Nickel-Phosphorus alloy (NiP). This alloy can be polished with computer assistance. Ion Beam Figuring (IBF) is the final manufacturing step. The properties after the finishing process are better than 1 nm rms for roughness and down to 15 nm rms respectively 100 nm p.-v. regarding the surface irregularity for complex optical shapes. The techniques SPDT, polishing and IBF ensures a high quality level for large mirrors with plan, spherical or aspherical surfaces. The manufacturing chain will be analyzed by surface characterisation based on 2D profilometry and white light interferometry to measure the roughness and 3D-profilometry and interferometry to monitor the shape irregularity. Scattering light analysis deepens these investigations. This paper summarizes technologies and measurement results for SPDT and surface finish of metal mirrors for novel optical applications.
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R. Steinkopf, A. Gebhardt, S. Scheiding, M. Rohde, O. Stenzel, S. Gliech, V. Giggel, H. Löscher, G. Ullrich, P. Rucks, A. Duparre, S. Risse, R. Eberhardt, A. Tünnermann, "Metal mirrors with excellent figure and roughness", Proc. SPIE 7102, Optical Fabrication, Testing, and Metrology III, 71020C (25 September 2008); doi: 10.1117/12.797702; https://doi.org/10.1117/12.797702
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