Improved ion beam tools for ultra-precision figure correction of curved aluminium mirror surfaces

Ion beam figuring with low-energy ion beam tools is a widely used finishing technique for most precise optical devices 1-3. For the machining of strongly curved 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 aperture-less constriction of ion beams in the low millimeter range. An oxygen ion beam with a full-width at half maximum (FWHM) of 4.0mm with an ion current density of 29.8mA=cm2 was achieved. 2) For even smaller ion beams a conic aperture design with a sub-millimeter sized exit opening has been tested. A nitrogen ion beam with a FWHM down to 0.62mm with an ion current density of 4.6mA=cm2 was obtained.