Introduction
From earlier, telescope is one kind of very mighty tools to help people study the remote space and stars. In order to study the detail of the remote space objective, telescopes which are used in scientific research needed very high spatial resolution. According to the Rayleigh criterion and Sparrow criterion, the angular resolution of the telescope is inversely proportional to the aperture diameter. So that large aperture telescope must be made in order to study the detail of the star, planet, nebula or faint source with sufficient energy[1].
When the telescope aperture is larger than 8m, the primary mirror or the second mirror of the telescope or both of them usually are divided into many segments or sub-apertures [2]. The Keck telescopes, with 1.8-m-diameter segments, and the Hobby-Eberly Telescope, with 1.15-m-diameter segments, are the only working multiple-mirror telescopes. OWL 100-rn optical telescope is actually discussions focused on the mirror feasibility issue [3]. The 8.4 m LBT mirrors. The mirror thickness varies from 437 mm at the inner edge to 894 mm at the outer edge. [4]. The Giant Magellan Telescope (GMT) uses seven 8.4-m diameter segments to create a giant primary mirror, 25 meters across with focal ratio f /0.7[5].
These sub-apertures are combined into a large mirror to reflect rays and acquire an image on the focusplane [6]. In addition, there is a potential for small segments to lightweight, low cost and easy to be support or using adaptive optics into telescope[7-9].
Synthesize of aperture by flat segments mirror
There many big telescopes were fabricated by the techniques of segments mirror in spherical or axis off aspheric surface to combine a whole large mirror. In this paper, we put forward a way to establish large telescope that is combining many flat segments mirror into one whole mirror. The structure of the primary mirror of this kind telescope could be showed in Fig. 1.
Collecting areas of the primary mirror of the telescopecould be calculated nearly by
In Eq. (1), Sprimary represents the surface area of the primary mirror diameter; and di represents diameter of the flat segments mirror projection on the rays′ direction, which is the pupil of the main lens;and also the a single segment mirror can be treated as a single sub-aperture or single sub-pupil of the telescope. N presents the numbers of the flat segments mirror.
In the Fig. 2, rays from remote source arrived to the “primary mirror” which combined (constituted) by many flat segments mirror. All the rays from remote source were reflected into main lens by the flat segments mirror. The first focal plane was the array of the images of the remote source, the flat segments mirror were arrayed and reflect the rays coming from the remote objective into the main lens. Also because the reflect angles which enter into the pupil is different from each segments mirror, so the image on the first image plane is the array images of the remote source.
Behind the array image plane, there is a lens array followed them; these array lenses collimated the array images in the first image plane, one image by one lens. After the rays were collimated, then the last lens behind them collects the collimated ray to focus the remote source into one image, and the remote source image should on the second focal plane.
Change of the primary mirror of this telescope
For any telescopes, the primary mirrors provided with power and aperture diameter which were used to collect rays energy and information from the remote source with high resolution. The power and aperture were combined by the primary mirrors in a whole, but this power and aperture of primary mirrors could be disjoined into independent parts. So the aperture could be constituted by many flat segment mirrors and the power could be provided by main lens instead. By this way, the diameter of aperture of the telescope primary mirrors could be enlarged more than its original size, and could acquire high resolution. The structure of the system could be showed as Fig. 3.
In the experiment, we used two flat mirrors were combined together as the primary mirror, using the collimated laser as the remote source (ZYGO interferometer) to illuminate the equipment from ahead, showed as Fig. 4, and get the small image, it was enlarged and showed in Fig. 5; the image acquired by the system using single flat mirror were showed in Fig. 6.
Theory discussion of synthesize aperture of this telescope
Usually, the synthesize aperture were applied in large optical telescope, in theory of the synthesize aperture, one point source wavefront of the remote object reach to the pupil of telescope often has the same path length, also is known as the same wave front. When the wave front was divided into many segments by the discrete primary mirror of synthesize aperture telescope. The segments wavefront must be focused into one point together and interference.
Define the single segment mirror pupil as
Suppose that each segments mirror in the telescope has its own PSFsub as
Andwhen all of them interference into together, then the final PSFfinal of the telescope could be acquired by
In Eq. (5), all the PSFsub of sub-aperture were collected together as one large aperture PSFsum, because all the PSFsub come from the same wavefront in theory, so all the rays which come to the same image point will occur interference, and get the PSFsum of the large telescope.
Outdoors photos by two channels telescope
Fig. 7 could be enlarged to see the detail, from the 2D FFT image, we can see the two channels photo has more frequency band than any one channel′s, so we could get the conclusion that high resolution could be reach by using multi-copying pupil of the optical system.
Conclusion
From the introduction and discussion above, the flat segments mirror could be used into the large telescope as a “primary mirror”. All the flat mirrors collect the one same field view by different channels and get more than one images of the same field view. By collimate the respect images, one large lens collect all the images rays into the one image, it is the synthesis image. And by the experiments outdoors, the synthesis image was proved as the super-resolution picture. One pupil multi-channel and super-resolution imaging optical system were provided as a conception by this system. The work principle of the system is made the system′s more field view to see the same subjects and every field view as one channel. And by this method the Flat mirrors could be used to assemble large telescope to acquire high resolution image. The weight of large telescope will be more lightened. And the proof of the super-resolution which two channel higher than anyone channel were gotten from the experiments.
Acknowledgement
In this paper, thanks all the people helped me, and especially Thanks XU Guang-zhou, LIU Xue-bin, YANG Jian-feng,etc ever supports for this project.