Wavefront Control for High Performance Coronagraphy on Segmented and Centrally Obscured Telescopes

The objective of our activity was to develop new high efficiency wavefront measurementtechniques for high contrast imaging on segmented and/or centrally obscured apertures.We have worked towards meeting the tight wavefront control requirements of a starlightsuppression system (SSS) aimed at direct imaging and characterization of Earth-like planetsaround other stars.
We have developed 5 new techniques for efficient high-performance wavefront control for highcontrast imaging :
(1) We have developed the differential Optical Transfer Function (dOTF) for accurate andpractical measurement of segment cophasing errors.
(2) We have produced a coronagraph system design combining high performance coronagraphyand Low-Order Wavefront Sensor (LOWFS) for segmented apertures. This achievement extendsthe previously developed LOWFS, which uses bright starlight rejected by the coronagraph, tofine control of cophasing errors in segmented apertures. 
(3) We have developed the Linear Dark Field Control (LDFC), a high efficiency alternative tothe previously used Electric Field Conjugation (EFC) wavefront control technique for highcontrast imaging. The technique uses bright speckles outside the dark hole to measure andcontrol wavefront errors. Its allows high contrast wavefront control to be ~30x more efficient than previously possible, and is ideally suited to track cophasing errors in a large segmented aperture.
(4) We have developed an algorithm for on-orbit system response self-calibration. 
(5) We have developed the self-calibrating coherent differential imaging (SC-CDI) technique,which allows recovery of incoherent (planet) light in bright speckles independently of the coronagraph system model errors. 
Techniques (3), (4) and (5) allow more robust high contrast wavefront control, which can adapt to minor differences between design and actual hardware (misalignments, contamination).We have also established a new highly flexible testbed at UofA that we have been using to validate new wavefront control approaches/concepts. The testbed uses a segmented deformable mirror to emulate a segmented aperture.