Optical testing of multi-electrode electrostatic membrane mirror

A membrane mirror prototype of 300 mm diameter was developed and optically tested. Basic optical parameters of membrane mirror were tested by Gaussian optics. The results show that relations between basic parameters of membrane mirror and the applied voltages are consistent with shaping theory. The surface shape characteristics and optical testing methods of membrane mirror are discussed. Laser interferometer was used to test the plat surface when voltages were zero, and the RMS (root mean square) value of surface error was 1.03 (=632.8 nm). Hartmann testing was used to test membrane mirror surface with radius, and the result shows that RMS value of surface error changes from 24.1 m to 14.7 m when different multielectrode voltages are used for optimization. This validates that multiple electrodes with different voltages optimize the surface accuracy of membrane mirror.