Wavefront distortion sensing for control of an adaptive optics system

By sensing the wavefront distortion in the propagation path, between an aperture and some distant point of interest, and using this information to control the deformation of some adaptive element in the optical train behind the aperture, it is possible to achieve nearly diffraction-limited performance in an imaging system viewing the point of interest through the aperture, or to achieve the same in a laser transmitter irradiating the point of interest through the aperture. The key to this process lies in the ability to sense accurately the wavefront distortion. Methods have been discussed in the published literature1,2 for directly sensing the random phase distortion at each point in the aperture relative to the aperture average phase. These methods have a noise sensitivity such that the error in the estimate of the wavefront distortion increases rapidly as the total aperture size, or the number of adjustment degrees of freedom encompassed by the aperture, increases. As a result, in many applications the useful aperture size of an adaptive optics system is significantly limited by SNR considerations in the wavefront distortion sensing.