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Proceedings Paper

Measurement And Interpretation Of Fine Form Errors In Optical Surfaces
Author(s): Jean M. Bennett
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Paper Abstract

Fine form errors, or surface microroughness, are localized height deviations of the actual surface from the ideal desired surface; in contrast, surface waviness has a longer spatial wavelength range (from a few millimeters to a centimeter) on the surface, and optical figure variations are height variations extending from approximately 1 cm to distances covering the entire surface. Surface microroughness produces scattering which degrades the performance of an optical system; thus, it is desirable to be able to measure it and then minimize it as much as possible. Another approach is to measure the scattering directly, either as a function of angle or as total integrated scattering (TIS) into a hemisphere. In this paper, methods for observing and measuring surface microroughness will be described, as well as methods for measuring TIS and angular scattering. The former include Nomarski microscopy, transmission electron microscopy, Fizeau and FECO (fringes of equal chromatic order) interferometry, optical heterodyne profilometry, and stylus profilometry. TIS can be measured using a light beam normally incident on an opaque reflecting sample and collecting all the scattering into a hemisphere, while angular scattering is most easily measured in the plane of incidence. Two other useful but more specialized techniques will also be described; total internal reflection microscopy (TIRM) is particularly useful for observing transparent filmed and unfilmed surfaces, while with ellipsometry small changes in the optical properties of a surface can be detected. By having the appropriate tools available for characterizing optical surfaces, it is possible to determine the effect of various surface preparation techniques so that the surface finishing process can be varied to produce higher quality optical surfaces.

Paper Details

Date Published: 10 November 1983
PDF: 19 pages
Proc. SPIE 0381, Optical Surface Technology, (10 November 1983); doi: 10.1117/12.934856
Show Author Affiliations
Jean M. Bennett, Naval Weapons Center (United States)


Published in SPIE Proceedings Vol. 0381:
Optical Surface Technology
Hermann Walter, Editor(s)

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