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Proceedings Paper

Checking the symmetry of stretchable plastic membrane concave mirrors using a lateral shearing interferometer
Author(s): Peter Waddell; Mathew Stickland; Stuart McKay; Leslie S. Mair
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Paper Abstract

The paper describes a simple to use and inexpensive lateral shearing interferometer for checking the symmetry of optically accurate stretchable plastic concave membrane mirrors. The same interferometer can be used for checking the optical flatness of tensional flat membranes, before they are stretched by air pressure difference into concave mirrors. The interferometer is also capable of examining a very wide range of mirror sizes and curvatures. The interferometer reveals by fringe distortion all the blemishes of the metallized mirror finish membranes. The smallest crease marks, invisible to the eye, now become visible. Dust particles can become trapped between the underside of the membrane circumference and the rim top of the membrane support frame. The particles are seen to greatly affect the fringes locally, but have no affect on the rest of the mirror. Slow changing fringes usually indicate leaks of air into the chamber behind the membrane, causing mirror curvature change; or they can indicate membrane creep. Membrane damping can be examined by shouting at the mirror from close range and noting the time for the fringes to resume their stationary positions. The same interferometer also makes a nice flow visualizer, a truly remarkable and well respected instrument.

Paper Details

Date Published: 15 November 1994
PDF: 10 pages
Proc. SPIE 2248, Optical Measurements and Sensors for the Process Industries, (15 November 1994); doi: 10.1117/12.194313
Show Author Affiliations
Peter Waddell, Univ. of Strathclyde (United Kingdom)
Mathew Stickland, Univ. of Strathclyde (United Kingdom)
Stuart McKay, Univ. of Strathclyde (United Kingdom)
Leslie S. Mair, Glasgow Caledonian Univ. (United Kingdom)


Published in SPIE Proceedings Vol. 2248:
Optical Measurements and Sensors for the Process Industries
Christophe Gorecki; Richard W. T. Preater, Editor(s)

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