Solar Multi-conjugate Adaptive Optics System Research Articles

Performance analysis and optimization of solar multiconjugate adaptive optics systems

ABSTRACT Multiconjugate adaptive optics (MCAO) stands as an essential technology for the development of future large-aperture solar telescopes. Its primary objective is to empower telescopes to achieve nearly diffraction-limited performance while substantially extending the correction field of view (FoV). Conventional solar MCAO relies on the combination of adaptive optics and high-altitude correction (AO + HAC) modules for multiconjugate correction. However, this architectural approach excels in correction performance primarily at the central position, with performance deteriorating as one moves farther from the centre. Consequently, it results in poor consistency of FoV correction performance. To address these limitations, a new architectural approach was introduced, which combines ground layer AO with HAC (GLAO + HAC). Preliminary results have shown that, compared to AO + HAC, this approach significantly enhances FoV correction uniformity. Building upon these initial findings, this paper undertakes a more extensive research of the GLAO + HAC system. Its objective is to compare various solar MCAO system architectures, including AO + HAC, GLAO + HAC, and general MCAO, to finally propose optimization tailored to GLAO + HAC. Through this analysis, the paper conducts the performance comparison between GLAO + HAC and general MCAO. It underscores that, under equivalent configuration parameters, the differences between these two systems are marginal. However, due to the advantage of the independent control of dual correction modules in GLAO + HAC, it can introduce an optimization strategy by increasing the number of subapertures at the cost of reducing the GLAO guide star sensing FoV. Finally, the results of this strategy demonstrate an obvious enhancement in performance and FoV correction consistency within the GLAO + HAC system.

Feasibility study of a layer-oriented wavefront sensor for solar telescopes: comment.

The future generation of telescopes will be equipped with multi-conjugate adaptive-optics (MCAO) systems in order to obtain high angular resolution over large fields of view. MCAO comes in two flavors: star- and layer-oriented. Existing solar MCAO systems rely exclusively on the star-oriented approach. Earlier we suggested a method to implement the layer-oriented approach, and in view of recent concerns by Marino and Wöger [Appl. Opt.53, 685 (2014)10.1364/AO.53.000685APOPAI1559-128X], we now explain the proposed scheme in further detail. We note that in any layer-oriented system one sensor is conjugated to the pupil and the others are conjugated to higher altitudes. For the latter, not all the sensing surface is illuminated by the entire field of view. The successful implementation of nighttime layer-oriented systems shows that the field reduction is no crucial limitation. In the solar approach the field reduction is directly noticeable because it causes vignetting of the Shack-Hartmann subaperture images. It can be accounted for by a suitable adjustment of the algorithms to calculate the local wavefront slopes. We discuss a further concern related to the optical layout of a layer-oriented solar system.

Feasibility study of a layer-oriented wavefront sensor for solar telescopes

Solar multiconjugate adaptive optics systems rely on several wavefront sensors, which measure the incoming turbulent phase along several field directions to produce a tomographic reconstruction of the turbulent phase. In this paper, we explore an alternative wavefront sensing approach that attempts to directly measure the turbulent phase present at a particular height in the atmosphere: a layer-oriented cross-correlating Shack-Hartmann wavefront sensor (SHWFS). In an experiment at the Dunn Solar Telescope, we built a prototype layer-oriented cross-correlating SHWFS system conjugated to two separate atmospheric heights. We present the data obtained in the observations and complement these with ray-tracing computations to achieve a better understanding of the instrument's performance and limitations. The results obtained in this study strongly indicate that a layer-oriented cross-correlating SHWFS is not a practical design to measure the wavefront at a high layer in the atmosphere.