Closed-loop control techniques for an adaptive-optical system with an interferometric wavefront sensor

摘要

The self-referencing interferometer (SRI) wavefront sensor (WFS) is being developed for applications requiring laser propagation in strong scintillation. Because it directly measures the optical field of the wavefront, the SRI WFS is less effected by scintillation than conventional WFSs. This feature also means the phase determined from the WFS measurements is limited to the range —π to π, due to the use of the arctangent function. If a segmented wavefront corrector is used, this constraint is not a problem. However, if a continuous facesheet deformable mirror is used, the resulting phase should be unwrapped in order to minimize fitting error. There are a couple of places in the adaptive-optical (AO) closed-loop control process where an unwrapping algorithm can be inserted. Simulations of these configurations have shown that how and where the unwrapping is carried out affects overall AO performance and loop stability. This paper presents an overview of the unwrapping options and the associated issues. A laboratory demonstration of two control loop configurations was carried out to test the validity of the simulation results. These experiments and their outcome are discussed.