Abstract
Aluminum mirrors offer great potential for satisfying the increasing demand in high-performance optical components for visible and ultraviolet applications. Ion beam figuring is an established finishing technology and in particular a promising technique for direct aluminum figure error correction. For the machining of strongly curved or arbitrarily shaped surfaces as well as the correction of low-to-mid spatial frequency figure errors, the usage of a high-performance ion beam source with low tool width is mandatory. For that reason, two different concepts of ion beam generation with high ion current density and narrow beam width are discussed. (1) A concave ion beam extraction grid system is used for apertureless constriction of ion beams in the low millimeter range. An oxygen ion beam with a full-width at half-maximum (FWHM) of 4.0 mm with an ion current density of 29.8 mA / cm2 was achieved. (2) For even smaller ion beams, a conic aperture design with a submillimeter-sized exit opening was tested. A nitrogen ion beam with an FWHM down to 0.62 mm with an ion current density of 4.6 mA / cm2 was obtained. In situ ion current density mapping is performed by scanning Faraday probe measurements. Special interest is set on the data evaluation for submillimeter ion beam analysis.
Highlights
Modern short-wavelength imaging systems in the visible and ultraviolet spectral range are based upon complex figured mirror devices with a spherical, aspherical, or free-form surface shape.[1]
It has been shown that the application of reactively driven, low-energy ion beam tools allows the direct figure error correction of mirror optics made from aluminum technical alloy materials AL6061 or AL905.5,6 Nontoxic gases as oxygen and nitrogen are used for ion beam processing
In contrast to the usual understanding of reactive ion beam etching (RIBE), no volatile reaction products are formed during operation
Summary
Modern short-wavelength imaging systems in the visible and ultraviolet spectral range are based upon complex figured mirror devices with a spherical, aspherical, or free-form surface shape.[1]. For the correction of waviness and microroughness errors, ion beam planarization is an established technique.[12] In particular, an ultrasmooth sacrificial layer is coated homogeneously onto the rough device surface. Bauer et al.: Improved ion beam tools for ultraprecision figure correction of curved aluminum mirror surfaces (a) (c). Ion beam planarization with reactive process control seems to be a promising technique for smoothing of aluminum mirror devices, in particular by the reduction of turning mark features and microroughness. Motion profile, the ion beam is moved deterministically along the device surface This approach allows the figure error correction of huge and diversely shaped mirror devices. The planar aluminum mirror has a concentric figure error profile as a result of the diamond turning process. Subaperture conceptions as the conventional pinhole aperture (Sec. 3.2) and a contraction aperture design (Sec. 3.3) are evaluated
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