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Numerical analysis of modal tomography for solar multi-conjugate adaptive optics

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Research in Astronomy and Astrophysics 2012年第4期12卷 465-471页

作者： Bing Dong de-qing ren Xi Zhang Physics ＆ Astronomy department California State University Northridge CA 91330-8268 USA National Astronomical Observatories/Nanjing Institute of Astronomical Optics ＆ Technology Chinese Academy of Sciences Nanjing 210042 China

Multi-conjugate adaptive optics （MCAO） can considerably extend the cor- rected field of view with respect to classical adaptive optics, which will benefit solar observation in many aspects. In solar MCAO, the Sun structure is utilized to provide multiple guide stars and a modal tomography approach is adopted to implement three- dimensional wavefront restorations. The principle of modal tomography is briefly re- viewed and a numerical simulation model is built with three equivalent turbulent lay- ers and a different number of guide stars. Our simulation results show that at least six guide stars are required for an accurate wavefront reconstruction in the case of three layers, and only three guide stars are needed in the two layer case. Finally, eigen- mode analysis results are given to reveal the singular modes that cannot be precisely retrieved in the tomography process.

关键词： instrumentation: multi-conjugate adaptive optics -- tomography

A low-cost and high-performance technique for adaptive optics static wavefront correction

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Research in Astronomy and Astrophysics 2021年第7期21卷 261-268页

作者： de-qing ren Tian-Yu Zhang Gang Wang California State University Northridge Department of Physics and AstronomyNorthridgeCA 91330USA National Astronomical Observatories/Nanjing Institute of Astronomical Optics and Technology Chinese Academy of SciencesNanjing 210042China CAS Key Laboratory of Astronomical Optics and Technology Nanjing Institute of Astronomical Optics and TechnologyNanjing 210042China University of Chinese Academy of Sciences Beijing 100049China

Non-Common Path Error(NCPE) is one of the factors that limit an Adaptive Optics(AO)system from delivering ultra-high performance. To correct the NCPE associated static aberration, we propose a simple but robust and high-performance pupil-plane based wavefront measurement and correction technique, which can copy a single-mode fiber generated perfect wavefront to the AO system via an iteration optimization process, and the NCPE can be effectively corrected by directly commanding the deformable Mirror(DM) of the AO system. Compared with the previous focal-plane based approach that uses focal plane based Point Spread Function(PSF) for correction evaluation, the pupil-plane based approach can be reliably and rapidly converged to a global optimization result and provides better performance, in particular for an AO system with a large initial static wavefront error. This technique we proposed can be implemented in astronomical AO systems where extremely high performance is required.

关键词： astronomical instrumentation:adaptive optics astronomical instrumentation:high angular resolution astronomical techniques:high angular resolution

Solar GLAO and TAO:performance comparisons

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Research in Astronomy and Astrophysics 2018年第7期18卷 125-132页

作者： de-qing ren Xi Zhang Si-Zhen Liu Physics&Astronomy department California State University NorthridgeNorthridgeCalifornia 91330USA National Astronomical Observatories/Nanjing Institute of Astronomical Optics&Technology Chinese Academyof SciencesNanjing 210042China Key Laboratory of Astronomical Optics&Technology Nanjing Institute of Astronomical Optics&TechnologyChinese Academy of SciencesNanjing 210042China University of Chinese Academy of Sciences Beijing 100049China

Multi-conjugate adaptive optics （MCAO）, consisting of several deformable mirrors （DMs）, can significantly increase the adaptive optics （AO） correction field of view. Current MCAO can be realized by either star-oriented or layer-oriented approaches. For solar AO, ground-layer adaptive optics （GLAO） can be viewed as an extreme case of layer-oriented MCAO in which the DM is conjugated to the ground, while solar tomography adaptive optics （TAO） that we proposed recently can be viewed as star-oriented MCAO with only one DM. Solar GLAO and TAO use the same hardware as conventional solar AO, and therefore it will be important to see which method can deliver better performance. In this article, we compare the performance of solar GLAO and TAO by using end-to-end numerical simulation software. Numerical simulations of TAO and GLAO with different numbers of guide stars are conducted. Our results show that TAO and GLAO produce the same performance if the DM is conjugated to the ground, but TAO can only generate better performance when the DM is conjugated to the best height. This result has important application in existing one-DM solar AO systems.

关键词： Adaptive Optics GLAO MCAO

High-contrast coronagraph for ground-based imaging of Jupiter-like planets

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Research in Astronomy and Astrophysics 2010年第2期10卷 189-198页

作者： Jiang-Pei Dou de-qing ren Yong-Tian Zhu National Astronomical Observatories / Nanjing Institute of Astronomical Optics ＆ Technology Chinese Academy of Sciences Nanjing 210042 China Key Laboratory of Astronomical Optics ＆ Technology Nanjing Institute of Astronomical Optics ＆ Technology Chinese Academy of Sciences Nanjing 210042 China Physics ＆ Astronomy department California State University Northridge 18111 Nordhoff Street Northridge California 91330-8268

We propose a high-contrast coronagraph for direct imaging of young Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a step- transmission filter in which the intensity is apodized with a finite number of steps with identical transmission in each step. It should be installed on a large ground-based telescope equipped with a state-of-the-art adaptive optics system. In this case, contrast ratios around 10-6 should be accessible within 0.1 arcsec of the central star. In recent progress, a coronagraph with a circular apodizing filter has been developed, which can be used for a ground-based telescope with a central obstruction and spider structure. It is shown that ground-based direct imaging of Jupiter-like planets is promising with current technology.

关键词： instrumentation: high angular resolution- methods: laboratory numer- ical -- techniques: coronagraphy apodization -- planetary systems

Two-telescope-based solar seeing profile measurement simulation

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Research in Astronomy and Astrophysics 2021年第12期21卷 305-314页

作者： Zi-Yue Wang de-qing ren Raffi Saadetian National Astronomical Observatories/Nanjing Institute of Astronomical Optics&Technology Chinese Academy of SciencesNanjing 210042China CAS Key Laboratory of Astronomical Optics&Technology Nanjing Institute of Astronomical Optics&TechnologyNanjing 210042China University of Chinese Academy of Sciences Beijing 100049China Physics&Astronomy department California State University NorthridgeCalifornia 91330-8268USA

Measurements of the daytime seeing profile of the atmospheric turbulence are crucial for evaluating a solar astronomical site so that research on the profile of the atmospheric turbulence as a function of altitude C_(n)^(2)(h_(n))becomes more and more critical for performance estimation and optimization of future adaptive optics(AO)including the multi-conjugate adaptive optics(MCAO)***,the S-DIMM+method has been successfully used to measure daytime turbulence profiles above the New Solar Telescope(NST)on Big Bear ***,such techniques are limited by the requirement of using a large solar telescope which is not realistic for a new potential astronomical ***,the AMASP(advanced multiple-aperture seeing profiler)method is more portable and has been proved that can reliably retrieve the seeing profile up to 16 km with the Dunn Solar Telescope(DST)on the National Solar Observatory(Townson,Kellerer et al.).But the turbulence of the ground layer is calculated by combining A-MASP and S-DIMM+(Solar Differential Image Motion Monitor+)due to the limitation of the twoindividual-telescopes *** solve these problems,we introduce the two-telescope seeing profiler(TTSP)which consists of two portable individual *** simulations have been conducted to evaluate the performance of *** find our TTSP can effectively retrieve seeing profiles of four turbulence layers with a relative error of less than 4%and is dependable for actual seeing measurement.

关键词： turbulence atmospheric effects sun:granulation

An active coronagraph using a liquid crystal array for exoplanet imaging:principle and testing

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Research in Astronomy and Astrophysics 2012年第5期12卷 591-600页

作者： Xi Zhang de-qing ren Yong-Tian Zhu Jiang-Pei Dou National Astronomical Observatories/Nanjing Institute of Astronomical Optics&Technology Chinese Academy of SciencesNanjing 210042China Key Laboratory of Astronomical Optics&Technology National Astronomical Observatories/Nanjing Institute of Astronomical Optics&TechnologyChinese Academy of SciencesNanjing 210042China Physics&Astronomy department California State University Northridge18111 Nordhoff StreetNorthridgeCalifornia 91330-8268USA Graduate University of Chinese Academy of Sciences Beijing 100049China

High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their best performance. To solve this problem, we propose a novel high-contrast imaging coronagraph which combines a liquid crystal array （LCA） for active pupil apodization and a deformable mirror （DM） for phase correction. The LCA we use is an amplitude-only spatial light mod- ulator. The LCA is well calibrated and compensates for its amplitude non-uniformity and nonlinear intensity responsivity. We measured the imaging contrasts of the coron- agraph system with the LCA only and without the DM deployed. Imaging contrasts of 10-4 and 10-5 can be reached at an inner working angular distance of 2.5 and 5A/D, respectively. A simulation shows that the phase errors on the coronagraph pupil limit the contrast performance. The contrast could be further improved if a DM is deployed to correct the phase errors induced by the LCA and coronagraph optics.

关键词： instrumentation: coronagraph liquid crystal array - techniques high-contrast imaging exoplanet detection

design and experimental test of an optical vortex coronagraph

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Research in Astronomy and Astrophysics 2017年第6期17卷 101-106页

作者： Cheng-Chao Liu de-qing ren Yong-Tian Zhu Jiang-Pei Dou National Astronomical Observatories/Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences Nanjing 210042 China Key Laboratory of Astronomical Optics & Technology National Astronomical Observatories/Nanjing Institute of Astronomical Optics & Technology Chinese Academy of Sciences Nanjing 210042 China Physics & Astronomy department California State University Northridge 18111 Nordhoff Street Northridge California 91330-8268 USA

Using an optical vortex coronagraph （OVC） is one of the most promising techniques for di- rectly imaging exoplanets because of its small inner working angle and high throughput. This paper presents the design and laboratory demonstration performance of an OVC based on liquid crystal polymers （LCPs） at 633 nm and 1520 nm. The OVC can deliver good performance in laboratory tests and achieve a contrast of 10-6 at an angular distance of 3A/D, which can be implemented for imaging young giant exoplanets in combination with extreme adaptive optics.

关键词： instrumentation coronagraph- techniques optical vortex - methods laboratory

A high-contrast imaging polarimeter with a stepped-transmission filter based coronagraph

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Research in Astronomy and Astrophysics 2016年第5期16卷 25-30页

作者： Cheng-Chao Liu de-qing ren Yong-Tian Zhu Jiang-Pei Dou Jing Guo National Astronomical Observatories/Nanjing Institute of Astronomical Optics&Technology Chinese Academy of SciencesNanjing 210042China Key Laboratory of Astronomical Optics&Technology National Astronomical Observatories/Nanjing Institute of Astronomical Optics&TechnologyChinese Academy of SciencesNanjing 210042China Physics&Astronomy department California State University Norihridge 18111 Nordhoff StreetNorthridgeCalifornia 91330-8268USA University of Chinese Academy of Sciences Beijing 100049China

The light reflected from planets is polarized mainly due to Rayleigh scattering, but starlight is normally unpolarized. Thus it provides an approach to enhance the imaging contrast by inducing the imaging polarimetry technique. In this paper, we propose a high-contrast imaging polarimeter that is op- timized for the direct imaging of exoplanets, combined with our recently developed stepped-transmission filter based coronagraph. Here we present the design and calibration method of the polarimetry system and the associated test of its high-contrast performance. In this polarimetry system, two liquid crystal variable retarders （LCVRs） act as a polarization modulator, which can extract the polarized signal. We show that our polarimeter can achieve a measurement accuracy of about 0.2% at a visible wavelength （632.8 nm） with linearly polarized light. Finally, the whole system demonstrates that a contrast of 10 9 at 5A/D is achievable, which can be used for direct imaging of Jupiter-like planets with a space telescope.

关键词： instrumentation: polarimeter coronagraph-- techniques: polarimetric -- methods: laboratory

Stochastic parallel gradient descent based adaptive optics used for a high contrast imaging coronagraph

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Research in Astronomy and Astrophysics 2011年第8期11卷 997-1002页

An adaptive optics （AO） system based on a stochastic parallel gradient descent （SPGD） algorithm is proposed to reduce the speckle noises in the optical system of a stellar coronagraph in order to further improve the contrast. The principle of the SPGD algorithm is described briefly and a metric suitable for point source imaging optimization is given. The feasibility and good performance of the SPGD algorithm is demonstrated by an experimental system featured with a 140-actuator deformable mirror and a Hartrnann-Shark wavefront sensor. Then the SPGD based AO is applied to a liquid crystal array （LCA） based coronagraph to improve the contrast. The LCA can modulate the incoming light to generate a pupil apodization mask of any pattern. A circular stepped pattern is used in our preliminary experiment and the image contrast shows improvement from 10^-3 to 10^-4.5 at an angular distance of 2A/D after being corrected by SPGD based AO.

关键词： instrumentation: adaptive optics -- methods: laboratory -- techniques: image processing coronagraph