27 December 2001 Precision optical asphere fabrication by plasma jet chemical etching (PJCE) and ion beam figuring
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Abstract
We develop a Plasma Jet Chemical Etching (PJCE) technique for high rate precision machining of optical materials aiming in a technology mature for precision asphere and free-form surface topology fabrication. The present contribution summarizes the achievements after about twelve months experience with a prototype production tool facility. PJCE is performed with the help of a microwave driven reactive plasma-jet working in a broad pressure range (10-600 mbar). We developed a moveable lightweight microwave plasma jet source for dwell time techniques performed in a roughly pumped process chamber equipped with a six axis system for precision workpiece and plasma source movement. Volume etch rates of some 10 mm3/min have been achieved for fused silica and silicon, respectively, using reactive (CF4,SF6,O2) and inert (Ar,He) gas mixtures and applying a microwave (2.45 GHz) power in the 100-200 W range. Large quartz plates (80-160 mm) have been figured using dwell time methods to achieve aspheric deformations of some 10 micrometers . The figured surfaces show shape errors of 1-2 micrometers and a microroughness of 50-100 nm RMS but no sub-surface damage enabling a small tool shape conserving post polishing up to the sub-nanometer roughness level. Thus, surface shaping to the nanometer error range can be done by ion beam finishing.
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Axel Schindler, Axel Schindler, Georg Boehm, Georg Boehm, Thomas Haensel, Thomas Haensel, Wilfried Frank, Wilfried Frank, Andreas Nickel, Andreas Nickel, Bernd Rauschenbach, Bernd Rauschenbach, Frieder Bigl, Frieder Bigl, } "Precision optical asphere fabrication by plasma jet chemical etching (PJCE) and ion beam figuring", Proc. SPIE 4451, Optical Manufacturing and Testing IV, (27 December 2001); doi: 10.1117/12.453622; https://doi.org/10.1117/12.453622
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