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Ultra-precise optical mirrors with thick amorphous silicon layer

: Risse, S.; Gebhardt, A.; Kolbmüller, A.; Steinkopf, R.; Schürmann, M.; Jobst, J.; Kaiser, N.; Eberhardt, R.

Spaan, H. ; European Society for Precision Engineering and Nanotechnology -EUSPEN-:
11th International Conference of the European Society for Precision Engineering and Nanotechnology 2011. Proceedings. Vol.2 : May 23rd - 26th 2011, Como, Italy; conference proceedings
Bedford: Euspen, 2011
ISBN: 978-0-9553082-9-1
European Society for Precision Engineering and Nanotechnology (EUSPEN International Conference) <11, 2011, Como>
Fraunhofer IOF ()

Metal mirrors with excellent optical, mechanical and thermal properties are used for a wide range of modern optical applications like telescopes, spectrometers or scanners. The surface quality of machined optical surfaces is one of the limiting factors in the manufacturing of ultra-precise optical components. Substrate materials like silicon can be polished very well and very smooth surfaces can be obtained. However, crystalline silicon is very hard and causes a large tool wear which makes the ultra-precise machining of silicon substrates difficult and expensive. Ductile substrate materials like Al, Cu of AlSi-alloys are much easier to machine, however, they cannot be polished to very low surface roughness. For reflective optics the state of the art is to overcome these limitations by deposition of electrochemical nickel-phosphorus (NiP) onto a machined substrate. The NiP layer can be polished much better than the diamond machined surface. A roughness below 1 nm rms can be achieved.
This paper discusses a new technology which is based on a amorphous silicon layer with a thickness of several microns deposited onto the surface. First results of diamond turned samples with polished surfaces are shown. This thick amorphous silicon layer can subsequently be polished and very smooth surfaces can be achieved.