A double-focus optical telescope (DOT) has been built for public observation and scientific research. The unique optical property of the DOT is that, both the Ritchey-Chretien (R-C) and Prime Focus systems are achieved on one telescope, using a common primary mirror. Switching between the R-C and Prime Focus systems is accomplished by moving the secondary mirror away from the optical path. The DOT also provides public observations through the eyepiece system.
The Fizeau type interferometric telescope forms an array of several sub telescopes for direct imaging on the image plane based on the principle of optical interferometry. Compared to the optical long baseline interferometer, this kind of telescope can be used for real time imaging of celestial body due to some excellent characteristics such as sufficient spatial frequencies coverage, single mounting avoiding outer optical delay lines and so on. We have built an interferometric imaging telescope with four apertures. Although each aperture size is 100mm, but this telescope can reach the higher angular resolution which is equivalent to a monolithic telescope of 280mm aperture size through optimal array configuration. Some novel opto-mechanical structure design and error control methods have been applied to this telescope successfully. For example, in order to enhance the rigidity of mechanical system, a unique C-shape structure to replace the traditional azimuth axis is adapted. Piston, tip/tilt errors between all apertures can be detected at the same time by extracting signals from Modulation Transfer Function (MTF), so some classical beam splitters can be removed which will reduce light loss significantly. At present, we have finished the final assembly, co-phasing calibration and verifying of dynamic co-phasing close-loop methods at laboratory. The FWHM of far field image spot is 0.43 arcsecond which is consistent with theoretical values. The out-door astronomical observation will be carried out soon.
Accurate piston error detection and closed-loop control are one of the key technologies to ensure the imaging quality of the interferometric imaging telescope. In this paper, we proposed a piston error detection and control scheme based on three computers and multithreading,which has been successfully applied to a four 0.1-m apertures interferometric telescope. This scheme adopts a kind of fringe contrast measurement and climbing method to achieve closed-loop control. The results implied that the fringe contrast can be raised through piston closed-loop correction. Compared with a single telescope with 0.1-m aperture, we can get a 2.63x improvement in resolution for the new interferometric telescope with four 0.1-m apertures. It is proved that the feasibility and effectiveness of this scheme. We will further carry out astronomical observation experiments and improve the piston error detection and control scheme, in order to provide technical guarantees for the implementation of interferometric imaging telescopes.
Large field-of-view rapid sky surveys are pivotal methodologies for research in time-domain astronomy. The project entitled ”Antarctic Time Domain Astronomical Optical Observational Array Based on Drift Scanning CCD Technology”, also known as the Antarctic Tianmu Plan, is based in Antarctica and comprises an assemblage of numerous small wide-field optical telescope systems. This expansive array covers a sky area of 10,000 square degrees. Each wide-field optical telescope unit is fitted with a low noise drift scanning CCD camera, facilitating rapid observations without the necessity of moving parts within the telescope system. The advantageous clear polar night conditions of Antarctica are employed to enable repeated and continuous wide-area observations, providing an optimal environment for the monitoring of transient events. A prototype of the Antarctic Tianmu Program was constructed from 2020 to 2022 and subsequently dispatched to the Zhongshan Station in Antarctica for installation, debugging, and operational observation in concurrence with the 39th scientific research vessel at the culmination of 2022. This manuscript primarily presents the quality of raw images and limiting magnitudes acquired at varying exposure times, observational results encompassing photometry precision, and the long-term stability of the system operation during the initial year of observation.
To achieve high-resolution image using optical synthesis aperture telescope, it’s necessary to co-phase accurately of all the telescopes so as to reduce the effect of co-phase errors including piston error, tip/tilt error, and mapping error, etc. Though simulation analysis of the optical system, error sources can be identified and thus save time of alignment. This paper introduces the Fizeau-type Y-4 prototype under development, including the layout of the Y-4 prototype, the layout of the reflective mirrors in the delayed light paths and the beam combiner. With the optical transfer function as the evaluation index, the actual equivalent diameter of Y-4 prototype is calculated. Furthermore, the effect of polarization introduced by coating and polarization differences on the contrast of interference fringe is analyzed. At present, the installation and alignment of the prototype in laboratory have been completed, and the interference synthesis of 4 light paths has been realized. One aim of this paper is to share some experiences in optical design and detection for the development of optical synthetic aperture telescopes. Another aim is to expand these new techniques to the larger optical synthesis aperture telescope project in the future.
Deformable mirror (DM) is the most main wavefront corrector in adaptive optics, which can be used to compensate optical aberrations through changing the reflective mirror’s surface frequently. However, a commercial piezoelectric DM can’t have an ideal flat initial surface under zero-voltage condition due to limitation of thin mirror fabrication and support structure of actuators behind of mirror. Optical aberrations generated by this initial distortion will seriously attenuate the performance of DM’s close-loop control, so a flat-surface calibration of mirror needs to be carried out before DM properly correct optical aberrations. In order to properly control the optical figure of the DM we have to obtain an interactive matrix which is the response of optical surface to the DM actuator’s stroke. We measured a serious of surface phase data of OKO 109-channel DM through self-collimation using a ZYGO-GPI interferometer directly, then construct the interactive matrix by zonal and modal methods. After several close-loop iterations, the initial RMS surface error of OKO 109-channel deformable mirror, 1.506λ has been remarkably reduced to 0.145λ.
Liquid rotating about a vertical axis takes a parabolic form, and can be used as the primary mirror in a reflecting telescope. It is a convenient way to get big primary mirror for astronomical telescope. But this kind of Newton type telescope with a parabolic surface has limited field of view, which is not capable for the detection of astronomical and orbital objects. It is necessary to design corrector lens with large field of view to improve the detection efficiency. In this paper, a prime focus corrector with a field of view of 2°, a focal length of 1.5 m, and wavelength coverage of 0.4-0.8 μm is designed for a liquid telescope with a clear aperture of 1 meter. The corrector is optimized by choosing different types of glass for achromatic design. The final corrector consists of 5 lenses and one filter, in which the largest one has a clear aperture of 280 mm and there is only one conic surface is used on a concave lens. The design result shows that 80% encircled energy is limited in one pixel, that is 12 μm for our F9000 3K×3K CCD camera, corresponding to 1.67″ resolution. The distortion is optimized to 0.01% which is very suitable for a Time Delay Integration (TDI) observation. The tolerance analysis for fabrication and assembly is also presented. Space debris and astronomical objects will be observed when the telescope is constructed.
In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wave-front sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in close loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full close loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.
Fringe test is the method which can detect the relative optical path difference in optical synthetic aperture telescope array.
To get to the interference fringes, the two beams of light in the meeting point must be within the coherence length. Step
scanning method is within its coherence length, selecting a specific step, changing one-way’s optical path of both by
changing position of micro displacement actuator. At the same time, every fringe pattern can be recorded. The process of
fringe patterns is from appearing to clear to disappearing. Firstly, a particular pixel is selected. Then, we keep tract of the
intensity of every picture in the same position. From the intensity change, the best position of relative optical path
difference can be made sure. The best position of relative optical path difference is also the position of the clearest fringe.
The wavelength of the infrared source is 1290nm and the bandwidth is 63.6nm. In this experiment, the coherence length
of infrared source is detected by cube reflection experiment. The coherence length is 30μm by data collection and data
processing, and that result of 30μm is less different from the 26μm of theoretical calculated. In order to further test the
relative optical path of optical synthetic aperture using step scanning method, the infrared source is placed into optical
route of optical synthesis aperture telescope double aperture. The precision position of actuator can be obtained when the
fringe is the clearest. By the experiment, we found that the actuating step affects the degree of precision of equivalent
optical path. The smaller step size, the more accurate position. But the smaller the step length, means that more steps
within the coherence length measurement and the longer time.
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