13 September 2012 Diamond milling of metal mirrors with optical surface quality
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Optical and opto-mechanical components in astronomical instruments are amongst the most expensive and delicate single parts. Lenses made of special glasses or crystals are sometimes difficult to obtain (if at all), especially with larger diameters and are figured and polished involving time-consuming and even risky procedures. At infrared wavelengths (< 5μm), when the instrument is cooled to temperatures even below that of liquid nitrogen, mechanical stress is induced between e.g. a glass lens and its metal mounting due to different heat expansion coefficients of the materials involved. This can considerably degrade the performance of the whole instrument. At infrared wavelengths the optical specifications considering surface roughness and form error are less tight than in the optical due to the longer wavelengths involved. Hence metal mirrors with a surface roughness and a form error of around 50 nm (RMS) may generally be favoured due to lower production costs then lenses. Goal of the project described here is to manufacture plane, spherical or aspherical aluminum mirrors, which are not hampered in the ways described above, in a cost effective procedure with optical specifications (surface roughness and form error) of less than 100 nm (RMS) by means of direct diamond milling.
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Christof Iserlohe, Andreas Eckart, Christian Straubmeier, Damian Moratschke, and Bernhard Brandl "Diamond milling of metal mirrors with optical surface quality", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84504V (13 September 2012); doi: 10.1117/12.925168; https://doi.org/10.1117/12.925168


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