Clearwidens the field for observations of the Sun with multi-conjugate adaptive optics

Abstract

The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasisimultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53 field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the images.

Advanced technologies and instrumentation and the National Science Foundation

“…Multi-Conjugate Adaptive Optics (MCAO) uses multiple wavefront sensors to achieve wide-field correction; notably 1407957/Goode recently led to the first demonstration of MCAO in solar imaging [18]. Extreme Adaptive Optics (ExAO) is a recent evolution of single-conjugated AO systems to achieve high contrast at short separations from a bright star for exoplanet searches [19].…”

Influence of speckle image reconstruction on photometric precision for large solar telescopes

“…A full or partial correction of wavefront distortions conjugated to the telescope pupil -as performed by conventional AO systems -does not affect the spatial decorrelation of modal Zernike coefficients describing these distortions (Molodij & Rousset 1997) across the field, as described by Wöger & von der Lühe (2007). Future MCAO systems (e.g., von der Lühe et al 2005;Berkefeld et al 2006;Schmidt et al 2017) aim to correct for discrete turbulent layers in earth's atmosphere using multiple correctors optically conjugated to the respective layer heights. Adapting this work to incorporate the correction by an MCAO system in the STF calculations requires knowledge of the remaining turbulence in the corrected and uncorrected layers so that the spatial decorrelation coefficients of the optical modes can be derived.…”

“…Furthermore, outside the isoplanatic path, the wavefront remains largely uncorrected because of the spatial decorrelation of atmospheric turbulence at different viewing angles. Multi-conjugate adaptive optics (MCAO) offer the potential to overcome the latter issue (e.g., von der Lühe et al 2005;Berkefeld et al 2006;Schmidt et al 2017), but residual errors will always be present to some degree. Reaching the diffraction limit both inside and outside the isoplanatic patch, therefore requires post-facto image reconstruction techniques such as multiobject multi-frame blind deconvolution (e.g., van Noort et al 2005) and speckle interferometry, the latter of which is the focus of this work.…”

Enabling discoveries: a review of 30 years of advanced technologies and instrumentation at the National Science Foundation

“…Recently, MCAO was first demonstrated for solar imaging at the Big Bear Solar Observatory as part of an ATI-supported research program (1710809/Goode). 59 Figure 9 is a result of this research; it illustrates the use of AO for improving solar observations and of the wider field of correction that is enabled by MCAO. Images were made at a 0.705 μm wavelength (corresponding to TiO spectral line) and have a 50 00 × 50 00 field of view.…”