Parametric assessment of material properties, boundary conditions and environmental effects on the performance of membrane optical systems

Abstract

Previous research has demonstrated the feasibility of manufacturing polymer membranes with surfaces suitable for use as optical elements on scales up to 1.5 meters. These membranes have optical surface finishes characterized by a roughness of 1.2 nanometers (rms) and mid spatial frequency figure errors (caused by thickness variations) of approximately 350 nanometers-adequate for many optical applications. With optical quality membranes fabrication demonstrated, the next technical challenges that must be met before large-aperture, ultra-light membrane mirrors can be practically achieved are to develop (1) light-weight deployable support structures, (2) the ability to control the global figure of large optical quality membranes, and (3) an improved understanding of the effects of membrane material properties (e.g., material in-homogeneities, coatings, and boundary conditions) on global figure. The work reported herein further characterizes several key system properties and their effects on optical aberrations. This analysis helps establish technical requirements for membrane optical systems and provides additional insight required to optimize deployable support structures capable of providing passive figure control for membrane optical elements. The results are also used to investigate the need for an electrostatic control system that can actively control the figure of a large membrane mirror.