Turbulence-induced Zernike aberrations of optical wavefronts in partial adaptive compensation

The residual phase error after correction for turbulence-induced phase aberrations by a partially compensating adaptive optics system with a laser guide star (LGS) as reference is computed by using the phase expansion on the Zernike polynomials. To get the most from the compensation, the limitation due to the actuator spacing of a deformable mirror, temporal lag and angular separation between the object and the LGS (anisoplanatism effect) have been analysed in this paper. If Fried's parameter r(0), is 10.7 cm, the temporal lag should be less than 2 ms for a sodium LGS. Also the higher the aberration radial degree is, the less the actuator spacing is required. To correct for aberration of radial degree higher than 4 (if r(0) is 10.7 cm), the actuator spacing should be less than 300 mm.