Mid-spatial frequency structure on an optical surface induces small-angle scatter in the transmitted wavefront. Freeform surfaces are particularly susceptible to mid-spatial frequency errors due to the sub-aperture nature of the fabrication processes. Several surface metrology methods that work for freeform surfaces use an indirect principle, reconstructing the surface shape from measured surface slope data. The integration process in the presence of measurement noise adds a spatial correlation to the dataset, leading to spurious spatial frequency structure. In this paper, we use the autocorrelation function to characterize and evaluate this artificial mid-spatial frequency structure on optical surfaces that are reconstructed by zonal integration methods.

Date Published: 18 August 2014
PDF: 7 pages
Proc. SPIE 9203, Interferometry XVII: Techniques and Analysis, 92030G (18 August 2014); doi: 10.1117/12.2061247

Published in SPIE Proceedings Vol. 9203:
Interferometry XVII: Techniques and Analysis
Katherine Creath; Jan Burke; Joanna Schmit, Editor(s)