Adaptive optics and multi-conjugate adaptive optics with the VTT

Abstract

We are currently developing adaptive optics (AO) system with a multi-conjugate extension for the German solar vacuum tower telescope (VTT) at the Teide Observatory on Tenerife.Multi-conjugate adaptive optics (MCAO) is a technique for increasing the field of view by compensating atmospheric turbulence along several, adjacent lines of sight. A conventional AO system compensates only a single line of sight in the direction of the lock point of its wavefront sensor. At larger field angles, the light from the source transverses higher layers of turbulence which are not sampled by the conventional system. Measurements at the VTT indicate that full compensation is typically restricted to a field of about 10 arcsec in diameter at visible wavelengths. An MCAO uses (at least) a second deformable mirror close to the focal plane of the telescope to compensate a larger field. The sun is a privileged target for an MCAO because the wavefront errors at larger field angles are easily measured. We intend to extend our existing AO system with a second deformable mirror and a second wavefront sensor which enables us to extend the compensated field by a factor of three in diameter.We present and discuss our concept.