Proceedings PaperAligning diamond-turned optics using visible-light interferometry
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A problem can arise when a set of optics must be aligned but intrinsic surface errors dominate alignment wavefront errors. Aligning diamond-turned optics interferometrically at visible wavelengths is one such example. Diamond-turned optics can exhibit a high-spatialfrequency surface ripple from the machining process, which, in many cases, can render an interferogram unintelligible to the point that even serious alignment errors cannot be detected. In an alignment demonstration conducted last year this problem was encountered head on and two techniques were applied to extract meaningful wavefront data. The first relied on spatial filtering of the return wavefront to smooth out the effects of high-slope surface errors. This approach showed potential in that it is a simple method that can be easily applied. The second approach used a new software algorithm, available as part of the Zygo Mark lV phase measuring interferometer, where regions of fringe discontinuities are discarded and the resultant piece-wise phase map is reconstructed as a continuous wavefront. Using this latter approach, we were able to precisely align a three-mirror telescope comprised of diamondturned mirrors and used in a double-pass configuration. The approaches to be described are applicable to the alignment of infrared and visible sensors and metrology of single surfaces.