In section 1. Letters
Clear widens the field for observations of the Sun with multi-conjugate adaptive optics
Adaptive optics has revitalized ground-based solar astronomy, by providing diffraction-limited resolution for large solar telescopes. The thickness of the tropospheric turbulent layers, however, limits the diffraction-limited field of view to approximately ten arcseconds when using a single deformable mirror and wavefront sensor. Multi Conjugate Adaptive Optics (MCAO) uses multiple deformable mirrors and wavefront sensors, each conjugated to a different atmospheric height, to produce wider diffraction-limited field of views, but has up to now been demonstrated only on stellar fields. Schmidt et al. obtained the first MCAO-corrected observations of the Sun with the Clear MCAO instrument on the New Solar Telescope, which also is the first three-layer MCAO system on any telescope. They demonstrate a well corrected field of view that is much widened, and therefore demonstrate that MCAO will be a critical component of future 4m-class solar telescopes.