| 摘要 |
Image-based, monochromatic, wavefront sensing for alignment of the segmented aperture of a telescope can produce segments which are misaligned by multiples of the center wavelength, lambda. The phenomenon is well-known and it is called "piston ambiguity" [1]. We call such a misalignment a "piston wrap." A segmented array, perfectly aligned except for piston wraps, will have perfect imaging at wavelength lambda but will have degraded imaging at other wavelengths. The present method detects and corrects piston wraps by making image-based measurements at a second wavelength lambda1. These measurements will produce an image of the piston-wrapped segments and the intensities of these segments are linearly related to the size of the piston wraps at wavelength lambda. 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 lambda to lambda1.
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