Imaging quality of segmented mirror synthetic aperture optics

The exit pupil wavefront of a segmented mirror Synthetic Aperture Optics (SAO) is discrete, and different from traditional system. To evaluate imaging quality, the theory of wave aberration and diffraction optics should be introduced simultaneously. By using the diffraction integral, two methods are used to evaluate imaging quality, one way is to fit the exit pupil wavefront to Zernike polynomial directly to calculate the complex amplitude distribution, and the other way is to calculate the complex amplitude distribution of each sub-exit-pupil individually, and overlap them in image plane. A segmented mirror system with three sub mirrors was built, and the wavefront was obtained by ZYGO GPIXP interferometer, including overall exit pupil wavefront and each sub-exit-pupil wavefront. By comparing the two methods, the result shows that the latter is more precise but complex; the former is more simple and can satisfy the required precision, when the system exit pupil wavefront is near the diffraction limit.