Integrated modeling of wavefront sensing and control for space telescopes utilizing active and adaptive optics

Abstract

Extreme wavefront correction is required for coronagraphs on future space telescopes to reach 10 -8 or better starlight suppression for the direct imaging and characterization of exoplanets in reflected light. Thus, a suite of wavefront sensors working in tandem with active and adaptive optics are used to achieve stable, nanometerlevel wavefront control over long observations. In order to verify wavefront control systems, comprehensive and accurate integrated models are needed. These should account for any sources of on-orbit error that may degrade performance past the limit imposed by photon noise.An integrated model of wavefront sensing and control for a space-based coronagraph was created using geometrical raytracing and physical optics propagation methods. Our model concept consists of an active telescope front end in addition to a charge-6 vector vortex coronagraph instrument. The telescope uses phase retrieval to guide primary mirror bending modes and secondary mirror position to control the wavefront error within tens of nanometers. The telescope model is dependent on raytracing to simulate these active optics corrections for compensating the wavefront errors caused by misalignments and thermal gradients in optical components. Entering the coronagraph, a self-coherent camera is used for focal plane wavefront sensing and digging the dark hole. We utilize physical optics propagation to model the coronagraphy's sensitivity to mid and high-order wavefront errors caused by optical surface errors and pointing jitter. We use our integrated models to quantify expected starlight suppression versus wavefront sensor signal-to-noise ratio.

Implicit electric field conjugation through a single-mode fiber

“…8,34 iEFC is also a promising control algorithm for space-based telescopes, as it eliminates the challenges associated with modeling on-orbit optical degradations. 24 Fig. 7 Final normalized intensity over a range of injected model errors for a Δλ∕λ 0 ¼ 30% bandwidth.…”

“…[21][22][23] Moreover, space-based telescopes too suffer from model uncertainties due to optical misalignments on-orbit caused by changing thermal gradients. 24 Implicit EFC (iEFC) utilizes a linear response between the DM and modulated intensity measurements, such that the reconstructed electric field is no longer computed explicitly. 22,25,26 iEFC is not the only measurement-based WFC technique.…”

Analysis of active optics correction for a large honeycomb mirror

“…This study is part of a larger simulation of the full active optics system for a large telescope, including wavefront sensing, alignment of M2 and bending of M1. 7 For the analysis presented in this proceeding, we assume tilt has been corrected by pointing the telescope, and focus and coma have been corrected by aligning M2. All remaining wavefront error will be addressed by bending M1 with its actuators.…”

“…A second 231-term Zernike fit to the corrected surface is fed back to the full simulation as M1's new surface shape. 7 Wherever a Zernike fit is used, we keep track of the fitting error (data minus fit) and consider it along with other analysis errors when we estimate the full system wavefront error. 9…”

“…Residual error therefore represents the limitations of the active control of mirror shape with a given number of bending modes and is not limited by sensor noise or phase retrieval algorithms used. 7…”