Adaptive optics for the support of exoplanet observations

Many programs and projects are underway to finally achieve the goal of directly observing planets outside of our solar system. All such observations will rely on the support of adaptive optics (AO). I will review the basic properties, benefits and parameters of such systems with respect to exoplanet observations. AO systems in support of direct imaging will be the prime focus, but I will also provide insight into the (potential) role of AO in other methods, such as astrometry and radial velocity observations. The critical role of AO in exoplanet observations is three-fold: AO has to enable the utilization of the telescope's full theoretical resolution. It also has to concentrate as much light as possible into a star's and planet's image core and remove it from the corresponding halos in order to enhance the achievable contrast limit. And last (but not least), the wavefront as such needs to be as flat as possible in order to enable devices like coronagraphs to efficiently remove the primary star's light. The latter two items combined result in a enormous dependence of finally achievable contrast from the so-called ``Strehl Ratio,'' the measure for wavefront flatness