Adaptive optics
The science of optical systems in which a controllable optical element, usually a deformable mirror, is used to optimize the performance of the system, for example, to maintain a sharply focused image in the presence of wavefront aberrations. A distinction is made between active optics, in which optical components are modified or adjusted by external control to compensate slowly changing disturbances, and adaptive optics, which applies to closed-loop feedback systems employing sensors and data processors, operating at much higher frequencies.
In a typical adaptive optics system (see illustration) the distorted light beam to be compensated is reflected from the deformable mirror and is sampled by a beam splitter. The light sample is analyzed in a wavefront sensor that determines the error in each part of the beam. The required corrections are computed and applied to the deformable mirror whose surface forms the shape necessary to flatten the reflected wavefront. The result is to remove the optical error at the sampling point so that the light passing through the beam splitter may be focused to a sharp image. Nonlinear optical devices are also capable of performing some adaptive optics functions; these devices operate at high optical power levels. See Aberration (optics), Geometrical optics, Nonlinear optics
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The practical development of adaptive optics started in the late 1960s. Its main applications have been to compensate for the effects of atmospheric turbulence in ground-based astronomical telescopes and to improve the beam quality of high-power lasers. Adaptive optics is now used routinely at several astronomical observatories.
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