Diffraction Limited Imaging in the Visible from Large Ground-Based Telescopes: New Methods for Future Instruments and Telescopes

Faint object diffraction limited imaging in the visible from the ground has recently been demonstrated on a 5 m telescope with more than twice the resolution of Hubble for the first time. It has shown the way towards diffraction limited imaging in the visible with the next generation of large telescopes. This paper describes the results of experiments to show how this is achieved and what is needed to work well with faint natural guide stars. The importance of a large isoplanatic patch size is also emphasised. In particular, we will describe a new approach to the design of high efficiency, low order adaptive curvature sensors which use photon counting CCD detectors. Such systems used on larger telescopes together with image segmentation and resynthesis techniques using closure phase techniques are shown to have an important place in achieving these goals. The optimum combination of these different techniques will be explained for a variety of different applications.