KEYWORDS: Adaptive optics, Solar telescopes, Wavefront sensors, Digital signal processing, Telescopes, Observatories, Turbulence, Field programmable gate arrays, Wavefronts, Image resolution
Multi-conjugate adaptive optics (MCAO) has been proved to obtain the high resolution images with a large field of view in solar observation. A solar MCAO experiment system had been successfully developed and tested at the 1-meter New Vacuum Solar Telescope (NVST) of Fuxian Solar Observatory. It consists of two deformable mirrors (DMs), a multidirection Shack-Hartmann wavefront sensor (MD-WFS), and a real-time controller. In order to command the two DMs, five guide regions were selected from the MD-WFS to retrieve a three-dimensional measurement of the turbulent volume based on atmospheric tomography. This system saw the first light in October, 2017, and a series of MCAO-corrected high resolution sunspots images were acquired. In this presentation, the MCAO experiment system is introduced, and the observation results are presented. Furthermore, a new MCAO system based on our proposed MCAO configuration with a high order ground layer adaptive optics and low order high altitude correction will be developed for the NVST as a regularly operating instrument for scientific observations of the sun.
Solar observations are performed over an extended field of view (FoV) and the isoplanatic patch which conventional adaptive optics (AO) provides diffraction limited resolution is a severe limitation. Multi-conjugate Adaptive Optics (MCAO) can be used to extend the corrected FoV of AO system. Compared to AO, MCAO which usually utilizes a wide-field Shack-Hartmann wavefront sensor to control multiple deformable mirrors(DMs) is more complicated. Because the Sun is an extended object, correlation algorithms are applied to detect gradients in solar MCAO system. Moreover, due to the fast evolving daytime seeing conditions and the fact that much science has to be done at visible wavelengths, a very high closed-loop bandwidth is also required. The computation and delay development of the real-time controller (RTC) in solar MCAO system is more challenging than that in night-time MCAO system. This paper reviews the solar MCAO techniques and systems in the world, especially emphasizes the framework and implementation of the RTC. The development of MCAO in China is also introduced. An outlook of the RTC for the solar MCAO system in development is given.
KEYWORDS: Adaptive optics, Solar telescopes, Observatories, Free space optics, Actuators, Digital signal processing, Telescopes, Imaging systems, Cameras, Mirrors
Adaptive Optics (AO) has become the requisite equipment of the ground-based large solar telescope to correct the wavefront aberration induced by the atmospheric turbulence. Two generation solar AO systems, one is the 37-element loworder AO system with 2100Hz frame rate and the other is 151-element high-order AO system with 3500Hz frame rate, were successfully developed in 2013 and 2015 respectively. In this presentation, the development of the two AO systems for 1-m New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO) will be introduced and the solar high resolution observational results are presented.
Solar observation with high resolution in large field of view (FoV) is required for some solar active regions with the typical sizes of 1’ to 3’. Conventional adaptive optics (AO) could not satisfy this demand because of the atmospheric anisoplanatism. Through compensating the turbulence in different heights, multi-conjugate adaptive optics (MCAO) has been proved to obtain a larger corrected FoV. A MCAO experimental system including a conventional 151-element AO system and a 37-element MCAO part is being developed. The MCAO part contains a 37-element deformable mirror conjugated into the 2km to 5km height and a multi-direction Shack-Hartmann wavefront sensor (MD-SHWFS) with 7×7 subaperture array and 60 arcsec FoV, the frame rate of the MD-SHWFS is up to 840Hz. Three-dimensional (3-D) wavefront sensing utilizing atmospheric tomography had been validated by solar observation. Based on these results, a ground layer adaptive optics (GLAO) experimental system including a 151-element deformable mirror and the MD-SHWFS has been built at the 1m New Vacuum Solar Telescope (NVST). In this paper, the MCAO experimental system will be introduced. The preliminary experimental results of three-dimensional wavefront sensing and GLAO on the NVST of Full-shine Lake Solar Observatory are presented.
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