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Proceedings Paper

Subaperture Testing For Mid-Frequency Figure Control On Large Aspheric Mirrors
Author(s): A. F. Slomba; L. Montagnino
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Paper Abstract

Encircled energy is an important specifying parameter for large, high quality optical telescopes and is critically dependent on the spatial frequency distribution of surface errors. Errors of surprisingly small amplitude whose spatial frequencies lie between those of the classical pupil aberrations and defects associated with the microroughness regime (i.e., whose periods lie below a millimeter) have a profound effect on encircled energy performance. This is particularly true at short wavelengths. Occurrence of this type of defect (called mid-frequency error) becomes more likely with increased mirror size. Full aperture interferograms that provide wavefront information over the pupil can lead to grossly inadequate performance predictions. Accurate prediction and the desired level of performance can only be achieved by precise measurement and control of the mid-frequency errors. This paper describes the processes and instrumentation for measuring and controlling figure error in this critical frequency domain during the manufacture of a high quality large aspheric mirror. Measurements of surface defects at the 0.002 µm rms level in the spatial frequency range of 0.01 to 0.25 cycle per millimeter are illustrated. The design and certification of a subaperture interferometer system is described.

Paper Details

Date Published: 15 November 1983
PDF: 5 pages
Proc. SPIE 0429, Precision Surface Metrology, (15 November 1983); doi: 10.1117/12.936347
Show Author Affiliations
A. F. Slomba, The Perkin-Elmer Corporation (United States)
L. Montagnino, The Perkin-Elmer Corporation (United States)

Published in SPIE Proceedings Vol. 0429:
Precision Surface Metrology
James C. Wyant, Editor(s)

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