FREEFORM MIRROR FABRICATION BY MEANS OF FAST TOOL SERVO DIAMOND TURNING

摘要

This study proves that diamond machining of an off-axis mirror as a freeform mirror in the center of rotation reduces the shape error nearly by the factor two. Error sources coming form the off-axis turning of the mirror, such as temperature induced influences or centrifugal forces can be reduced. Moreover the freeform machining allows the shape error correction of the non-rotationally symmetric error share. The aggressive lightweight structures of the mirror show no influence on the shape deviation. The diamond milled reference elements and mechanical interfaces allow the alignment of the mirror for measurement and integration processes with micrometer precision. Tilted interfaces are used for the re-transformation of the off-axis surface. The shape irregularities in the CA satisfy the Marechal condition for NIR-MIR-FIR optics starting at a wavelength of 1.4 μm. For these spectral ranges the mirror is considered to be diffraction limited.