Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21932801g&link_type=abstract
American Astronomical Society, AAS Meeting #219, #328.01
Astronomy and Astrophysics
Astronomy
Scientific paper
Future space-based coronagraphs will require focal plane wavefront control techniques to achieve the necessary contrast levels to achieve an earth-like planet detection. These correction algorithms are iterative and the control methods require an estimate of the electric field at the science camera. The Stroke Minimization algorithm developed at the Princeton High Contrast Imaging Laboratory has proven symmetric dark hole generation using minimal stroke on two deformable mirrors (DM) in series. We extend the concept of minimizing DM actuation to achieve symmetric dark holes in broadband light, thus minimizing the number of exposures required to obtain a spectra. Since it is the estimation step that uses the majority of the images in the correction algorithm, we make the broadband suppression problem more efficient in two ways. The first is to use a model based extrapolation technique so that the broadband suppression algorithm only requires a single monochromatic estimate of the electric field. Second, we reduce the number of exposures in the field by employing state estimate feedback in the form of a Kalman filter. The Kalman filter formalism guarantees that the estimate becomes near-optimal with regard to actuation and sensor noise. Implementation of the Kalman filter also allows for parameter adaptive control, which will increase the robustness of the control algorithm to disturbance. Optimality of the entire problem can also be addressed through the use of a dual controller, allowing the algorithm to perturb or suppress the field in an optimal way so that the final high contrast levels can be achieved with the fewest exposures possible. We present experimental and theoretical progress of these estimation and control problems for high contrast imaging. This work is funded by NASA Grant #NNX09AB96G and the NASA Earth and Space Science Fellowship.
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