Laser guide star (LGS) wavefront sensing (WFS) is insensitive to tip/tilt, and the variability of the sodium layer altitude in the atmosphere compromises focus measurements. Consequently, sensing of tip/tilt and focus needs to be done separately by means of faint natural guide stars (NGS). In this article, we study and compare three different single-image-phase-diversity (SIPD) algorithms for this specific application, namely Gerchberg-Saxton (GS), Linearized Focal Plane Technique (LiFT), and Fast&Furious (F&F) using high-fidelity Monte Carlo simulations. We present a complete study regarding the performance of GS, LiFT, and F&F under realistic conditions of flux, SNR, and sampling. In addition, we also used these algorithms to measure non-common path aberrations (NCPA), pupil fragmentation modes, and primary mirror phasing errors.
|