27 December 2001 Precision optical asphere fabrication by plasma jet chemical etching (PJCE) and ion beam figuring
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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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