A non-linear curvature wavefront sensor for the Subaru telescope’s AO3k system

A few years ago, we started upgrading AO188 into AO3k, including the real-time control system, laser guide star system, Deformable Mirror (DM), and Wavefront Sensors (WFSs). In this paper, we present the development of a non-linear Curvature WFS (nlCWFS) as a new visible WFS for the upgraded AO3k system. We also introduce the optical and optomechanical design of the nlCWFS. The nlCWFS has two new features: one is the dual-stroke linear mode, and the other one is to deploy non-linear wavefront reconstruction. The dual-stroke linear mode provides a good sensitivity for both low- and high-order aberrations. Also, the non-linear wavefront reconstruction provides a large dynamic range. By combining the linear and non-linear methods, the nlCWFS takes both advantages. Finally, we present laboratory demonstration results of closed-loop experiments in the lab with linear and non-linear wavefront reconstruction algorithms.