Adaptive Optics for Extremely Large Telescopes

Adaptive Optics (AO) has become a key technology for the largest ground-based telescopes currently under, or close to beginning of, construction. AO is an indispensable component and has basically only one task, that is to operate the telescope at its maximum angular resolution, without optical degradations resulting from atmospheric seeing. Based on three decades of experience using AO usually as an add-on component, all extremely large telescopes and their instrumentation are designed for diffraction limited observations from the very beginning. This paper illuminates various approaches of the ELT, the Giant Magellan Telescope (GMT), and the Thirty-Meter Telescope (TMT), to fully integrate AO in their designs. The paper concludes with a brief look into the requirements that high-contrast imaging poses on AO.