Phase Retrieval And Diversity In Adaptive Optics

Abstract

It is pointed out that wavefront sensing by phase retrieval implies extraction of the Fourier transform of a complex signal based on observation of the modulus of the signal. For estimating the phase aberrations, only the image intensity from a system's focal plane array is required. These estimates are used in deriving control signals to align (or to maintain alignment of) the optical system. The concept is applicable to both a predetection and postdetection mode. With the former, the control system works to keep the optics in a diffraction-limited mode all the time; with the latter, the control system induces a phase or wavelength diversity that allows successive images to be restored to nearly diffraction-limited quality by postprocessing of the image. This second mode is considered particularly interesting because it will reduce the design effort for both the optical system and the control system. The mathematics of the technique is described, and some computer simulations that involve both point sources and extended objects are shown.