Requirements of deformable mirrors for adaptive optics

An adaptive optics (AO) system is one that is capable of correcting dynamic distortions and aberrations in an optical image or beam. There are three keys elements in a "conventional" AO system: the wavefront sensor, the correction device ("deformable mirror", DM), and a control system. The fundamental limits of AO are usually governed by the noise in the wavefront sensor, but the practical limit is often set by the correction device. Possible correction devices include: piezo-stack mirrors, bimorph mirrors, membrane mirrors, MEMS mirrors and refractive or reflective liquid crystal spatial light modulators. The temporal response required of deformable mirrors is strongly application dependent, varying from perhaps a few Hz in vision science to several KHz in strong turbulence. A parameter of special significance when thinking about MEMS mirrors is the physical size of the device. The DM is placed in a plane conjugate to the plane of the aberration (this might be the pupil plane in some cases), and the ratio of the diameter of the device to that of the correction area (e.g. pupil) determines the (de-)magnification M: however, angles in the pupil are then magnified by a factor M on the DM