By placing a mask over the pupil of the optical telescope, the aperture masking technique transforms the telescope into a Fizeau interferometry telescope. Thanks to reasonable aperture configuration and baseline rotation techniques, it is possible to achieve almost the same imaging quality as a full aperture telescope. This technique has shown great potential in astrometry and astrophysics research, such as: exoplanet detection, protoplanetary disk, brown dwarf, etc. In order to verify the image restoration algorithm, we carried out binary stars observations on 1.56-m telescope. We presented the numerical simulation of aperture configuration and baseline rotation, and designed the mask and the experimental system. We select some binary stars with magnitude from 5 to 7 and angular distance from 0.2 to 2arcsec as observation targets. Combined with the short exposure observation, a two-step image restoration method is proposed, the results of high-resolution image reconstruction and angular distance measurement are verified. The above results will be applied to the first-generation Fizeau interferometry prototype at the Shanghai Astronomical Observatory (SHAO).
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.
In general, most of the adaptive optical systems for human eye aberration detection are based on the wavefront slope measurement provided by the Shark-Hartman wavefront sensor (SHWS), and then the wavefront slope is fed back to the deformable mirror to correct the human eye aberrations. Compared with the SHWS, the pyramid wavefront sensor (PWS) has the characteristics of fast sampling speed, wide linear capture range, and high sensitivity. Our works show that the modulation angle of the dynamic high-frequency modulator affects the dynamic measurement range, linearity and sensitivity of the pyramid sensing. The dynamic measurement range and the linear fitting residuals are both proportional to the modulation angle, and the sensitivity is inversely proportional to the modulation angle. Pixel combination affects the sensitivity of the detection signals of the pyramid sensor. The pixel combination mode of 1 × 1, 2 × 2, and 3 × 3 is tested respectively. When the pixel combination mode of 2 × 2 is used, the sensitivity of the signals will be highest significantly. In addition, the beacon light used to detect the human eye should not be too strong. The grinding “blind zone” of the spires and edges will have a scattering effect on the incident light and cause loss of light energy. Therefore, it is necessary to optimize the parameters of the pyramid sensor and further improve the processing technology of the pyramid prism.
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.
High resolution observation of celestial objects has always been the goal of optical interferometry. In this paper, we concentrated on two aspects of image reconstruction for Fizeau interferometric telescope. 1. The influence of piston error on imaging quality was studied, which provides a basis for the technical specifications of telescopes. 2. We proposed to use speckle imaging technology in interferometric telescopes, this method can reduce the effect of atmospheric turbulence on the resolution. In summary, a method combining denoising algorithm and speckle imaging technology is used to suppress noise, remove turbulence and reconstruct high-resolution images of real objects. The simulation results show that speckle imaging technology is also applicable to the interferometric telescope, and got good image reconstruction effect. The research results can be further extended to other mosaic telescopes.
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.
Speckle interferometry has beenwidely used in the observational astronomy, especially in binary stars.This paper is the
part of a series dedicated to the speckle imaging of binary stars carried out by the research team of Shanghai
Astronomical Observatory.The observation experiments were carried out with 1.56-m telescope using a speckle
camera,and the high resolution image were reconstructed successfully using speckle interferometry and iterative shiftand-
add. In order to speed up the computation speed, we also prepared a reconstruction software based on GPU
technology and CUDA programming model, compared with C++ program based on CPU, the speed ratio can reach
about 7 times.
Fizeau interferometry is one of the most important technique to measure astronomical objects with high angle resolution.
This paper is the part of a series dedicated to research of the Fizeau interferometry carried out by the research team of
Shanghai Astronomical Observatory. This paper is mainly concerned the simulation of image restoration based on
Y-type telescope and segmented mirrors telescope. It is proved that we can get the high resolution image using RL and
OS-EM method.
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