High-order AO in the visible, a particular niche for 4m-class telescopes?
Richard Myers, Alastair Basden, Nazim Bharmal, Nigel Dipper, Tim Morris
The analysis of the Durham High-Order Demonstrator (DHOD) design is presented, to explore the possibility of XAO on small/4m telescopes. It does not offer the same scientific goals as XAO being deployed on 8m telescopes, such as exoplanet detection. Instead it is designed to offer itself as an on-sky technical test-bed for developing high-order AO in itself with associated control system development, together with the ability to test arbritrary coronographic technologies for enhancing imaging contrast. By designing a flexible test-bed based on the experience of the Durham group, DHOD offers a particular opportunity for instrument development that encompasses both high-order AO and high-contrast imaging. A particular design feature is the Complex Amplitude Sensor, which is designed to measure non-common path errors in order to characterise the AO-corrected PSF. The design is explained in detail and expected limiting performance estimates are displayed along with investigations of PSF characterisation taking into account realistic telescope errors such as misalignments and vibrations.