Elimination of piston wraps in segmented apertures by image-based measurements at two wavelengths

Abstract

A segmented array, perfectly aligned except for piston wraps, will have perfect imaging at wavelength λ but will have degraded imaging at other wavelengths. The present method detects and corrects piston wraps by making image-based measurements at a wavelength λ and a second wavelength λ. These measurements will produce an image of the piston-wrapped segments and the intensities of these segments in the image at wavelength λare linearly related to the sizes of the piston wraps at wavelength λ. The method needs no additional equipment like inter-segment apertures, lenslets, and detectors. It needs only a narrowband filter to change the measurement wavelength from λ to λ.