A flexible testbed for adaptive optics in strong turbulence

Abstract

In recent years, optical wave propagation through strong atmospheric turbulence and adaptive optics compensation thereof has received much attention in literature and technical meetings. At the Air Force Institute of Technology, recent simulation-based efforts in strong turbulence compensation are expanding into laboratory experiments utilizing a versatile surrogate turbulence simulator and adaptive optics system. The system can switch between using two different wavefront sensors, a Shack-Hartmann and a self-referencing interferometer. Wavefront reconstruction takes place on field programmable gate arrays, operating at kilohertz frame rates. Further, the system is able to perform reconstruction and control in software for testing of advanced algorithms (at frame rates below 10 Hz). The entire package is compact enough for transportation to other laboratories and live test facilities. This paper describes the optical layout, architecture, and initial results of real-time operation.

Comparison of branch point tolerant wavefront reconstructors in the presence of simulated noise effects

“…The system uses a tracking loop to correct tilt and a separate control loop for higher-order aberrations. A thorough description of AFIT's AO system can be found in [2]. For this research, only the SRI is used for higher-order sensing due to the SRI's theoretical immunity to scintillation effects which degrade other WFS technologies [10].…”

“…At the simulation start, the AO system is completely off, followed by the tracker coming online at 0.01s, and subsequently the high-order correction at 0.02s. Our initial implementation of the LSPV reconstructor used a tilt-removed LS reconstructor in both (1) and (2). However, the SRI measurements contain the residual tilt (not corrected by the FSM), and when a tilt-removed LS reconstructed phase is subtracted from the wrapped-phase SRI measurement, the output of (2) once again contains tilt.…”

“…This approach is called adaptive optics (AO), utilizing a wavefront sensor (WFS) and reconstructor to estimate the optical distortions on some reference beam followed by a wavefront corrector to mitigate the estimated distortions. At the Air Force Institute of Technology (AFIT), a new AO system has been built to research novel AO techniques for realistic applications [2]. Section 2 presents a brief introduction to branch points and the problems they cause for AO.…”