Layer-oriented adaptive optics for solar telescopes

Abstract

with the permission of OSA. The paper can be found at the following URL on the OSA website:http://dx.doi.org/10.1364/AO.51.005743. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80 arc sec in diameter. We propose to implement the layeroriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems.

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

“…In the solar approach the lenslets of the SH wavefront sensor produce field images, which are then cross correlated to determine the average phase shifts over the field [3]. The field reduction becomes apparent as vignetting in these images.…”

“…As an alternative to the star-oriented approach we have proposed a layer-oriented setup for solar MCAO [3]. In the star-oriented approach the lenslets of the SH sensors are conjugated to the telescope pupil.…”

Solar Ground-Layer Adaptive Optics

“…As discussed by Marino and Wöger (2014) and Kellerer (2014), when a SHWFS is conjugated to a distance away from the telescope aperture, the SHWFS images are vignetted and the effective wavefront sensing FOV is reduced. Here, we present a quantitative calculation for the vignetting and FOV reduction, and this process is shown in Figure 3.…”

“…Marino and Wöger (2014) pointed out that in solar layer-oriented MCAO, the Shack-Hartmann wavefront sensor (SHWFS) images are vignetted. As explained in Kellerer (2014), this requires an adjustment of the correlation algorithms to determine the local wavefront slopes. Marino and Wöger further suggest that the method is not viable due to field reduction at high-conjugate layers.…”

“…Marino and Wöger further suggest that the method is not viable due to field reduction at high-conjugate layers. This issue is likewise addressed by Kellerer (2014): Field reduction is inherent to the layer-oriented approach. It particularly affects nighttime systems because the signal is averaged over a limited number of stars, rather than a continuous field.…”