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Proceedings Paper

Effects Of Coating Thickness Non-Uniformities On The Polarization And Optical Figure Properties Of Large Mirrors (~4 Meters)
Author(s): Wasim Hasan; Bruce A. Tirri
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Paper Abstract

There is growing interest in using larger primary mirrors (3- to 4-meter diameter range) as the output optic in various laser systems. A major advantage of this approach is a reduction in the thermal blooming problem when laser beams are transmitted through the atmosphere. Another significant advantage is the increase in focussed intensity, which becomes available if non-uniformities of coatings can be kept to a certain limit. The thickness non-uniformities are caused by the vacuum coating chamber's physical constraints and the coating process. These non-uniformities manifest themselves in three ways, i.e., 1) as variation in spectral reflectivity performance over the clear aperture; 2) as variation in polarization state properties of the coating over the clear aperture; and 3) as figure distortions. This paper deals with the physical constraints of the coating chamber that controls the non-uniformities in thickness and how these thickness non-uniformities affect the polarization and optical figure properties of a coating design. A simplistic coating design is initially selected for a set of two wavelengths and its optical performance over the clear aperture of a 3.6-meter optic is given along with the effect on the optical figure. It was found that this initial design produces phase distortion of opposite signs at the two wavelengths. This causes a problem in that, if the misfigure is partially corrected by focussing for one wavelength, this will aggravate the misfigure for the other wavelength. It has been shown in this paper that a modified, still simplistic design (full- or half-quarter wave design) can be used to correct this problem without appreciably affecting the reflectivities at the wavelengths of interest.

Paper Details

Date Published: 25 January 1990
PDF: 8 pages
Proc. SPIE 1166, Polarization Considerations for Optical Systems II, (25 January 1990); doi: 10.1117/12.962902
Show Author Affiliations
Wasim Hasan, The Perkin-Elmer Corporation (United States)
Bruce A. Tirri, The Perkin-Elmer Corporation (United States)

Published in SPIE Proceedings Vol. 1166:
Polarization Considerations for Optical Systems II
Russell A. Chipman, Editor(s)

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