EVALUATION OF LEAST-SQUARES PHASE-DIVERSITY TECHNIQUE FOR SPACE TELESCOPE WAVE-FRONT SENSING

Because of mechanical aspects of fabrication, launch, and operational environment, space telescope optics can suffer from unforeseen aberrat ions, detracting from their intended diffraction-limited performance g oals. We give the results of simulation studies designed to explore ho w wave-front aberration information for such near-diffraction-limited telescopes can be estimated through a regularized, low-pass filtered v ersion of the Gonsalves (least-squares) phase-diversity technique. We numerically simulate models of both monolithic and segmented space tel escope mirrors; the segmented case is a simplified model of the propos ed next generation space telescope. The simulation results quantify th e accuracy of phase diversity as a wave-fron sensing (WFS) technique i n estimating the pupil phase map. The pupil phase is estimated from pa irs of conventional and out-of-focus photon-limited point-source image s. Image photon statistics are simulated for three different average l ight levels. Simulation results give an indication of the minimum ligh t level required for reliable estimation of a large number of aberrati on parameters under the least-squares paradigm. For weak aberrations t hat average a 0.10 lambda pupil rms to a best case of only 0.002 lambd a pupil rms, depending on the light level as well as on the types and degrees of freedom of the aberrations present. (C) 1997 Optical Societ y of America.