Ground-based adaptive optics coronagraphic performance under closed-loop predictive control

Abstract

The discovery of the exoplanet Proxima b highlights the potential for the coming generation of giant segmented mirror telescopes (GSMTs) to characterize terrestrial -potentially habitable -planets orbiting nearby stars with direct imaging. This will require continued development and implementation of optimized adaptive optics systems feeding coronagraphs on the GSMTs. Such development should proceed with an understanding of the fundamental limits imposed by atmospheric turbulence. Here we seek to address this question with a semi-analytic framework for calculating the post-coronagraph contrast in a closed-loop AO system. We do this starting with the temporal power spectra of the Fourier basis calculated assuming frozen flow turbulence, and then apply closed-loop transfer functions. We include the benefits of a simple predictive controller, which we show could provide over a factor of 1400 gain in raw PSF contrast at 1 λ/D on bright stars, and more than a factor of 30 gain on an I = 7.5 mag star such as Proxima. More sophisticated predictive control can be expected to improve this even further. Assuming a photon noise limited observing technique such as High Dispersion Coronagraphy, these gains in raw contrast will decrease integration times by the same large factors. Predictive control of atmospheric turbulence should therefore be seen as one of the key technologies which will enable ground-based telescopes to characterize terrrestrial planets.

Characterizing vibrations at the Subaru Telescope for the Subaru coronagraphic extreme adaptive optics instrument

“…An adaptive Linear Quadratic Gaussian (LQG) controller was implemented and showed promising results, 6 while a more robust predictive control is also currently tested on SCExAO. 16,17 A increased communication between AO188 and SCExAO will soon help the correction of strong vibrations, by offloading part of the correction to AO188's higher stroke DM. Finally, future techniques like sensor fusion, which merges measurements from multiple wavefront sensors and accelerometers to compute an optimal correction, will also be implemented in the future, and should improve the correction of strong vibrations.…”

MagAO-X: project status and first laboratory results

“…In Figure 4 we show gain maps for the Fourier basis, optimized using the framework developed in Ref. 31. The size of the modal basis in spatial frequency space is indicated for 1K and 2K DMs, demonstrating that the choice of a 2K DM is well justified by our science case and performance requirements.…”

Single conjugate adaptive optics for the ELT instrument METIS

“…20, the residual tilt amplitude does not exceed the 5 mas rms requirement. We expect that even better vibration compensation including predictive control is possible [48][49][50].…”