Optical quality membrane mirror

Abstract

This thesis describes the development of an optical quality membrane mirror with aberrations smaller than the correction limit of an adaptive optical mirror. The shape is generated by a pressure difference. A small overview about historical and state-of-the-art membrane mirrors is given. Hencky’s respec-tively Campbell’s approximations are the most used theories for describing the deformation of a thin membrane subjected to uniform pressure. The main wavefront error is spherical aberration. Shape correction is possible by varying design-parameters or by using adaptive optical systems. Suitable materials are polyester and polyimide. A solar safety film is used for our membrane mirrors. Mechanical and optical properties were determined with experiments. Because the prototype DLR-AOS per-formed poorly, the influence of the initial tension was analyzed. The component creating this tension was replaced by a more satisfying pellicle frame adjustable in 5 axes. The point spread function im-proved significantly. A flexible experimental setup for measuring the deviation from a reference sphere with interference respectively Shack-Hartmann-sensor was designed. Integration of the adap-tive mirror is prepared. The wavefront deviation is within 10 λ (λ = 633 nm) and very smooth. 6 λ are achievable by adjusting the pellicle frame. The dominant wavefront errors are astigmatism and coma caused by non-ideal boundary conditions