An analysis of membrane mirrors for use in large aperture imaging systems

The finite element model was used to determine the surface figure of membrane mirrors. The Poisson's ratio of the membrane was varied to determine the most desirable materials. It was found that materials with a Poisson's ratio of 0.45 or greater are desirable. Membranes mirrors alone are poor imaging surfaces, and the effects of radial boundary displacement are investigated. It was found that radial boundary displacement can reduce the r.m.s. wavefront error of a 42 inch diameter f/1.9 mirror by 78.7%. A 42 inch diameter f/1.06 membrane mirror would have the r.m.s. wavefront error reduced by 65.6%. The primary on-axis and off-axis aberration was found to be 3/sup rd/ order spherical aberration for all f-numbers and at all radial displacements.