From Event: SPIE Optical Engineering + Applications, 2017
The Wide-Field Infrared Survey Telescope (WFIRST) is a 2.4m diameter space telescope NASA program. The payload will include a coronagraph instrument (CGI). The CGI designs under development use deformable mirrors (DM) to create a point spread function (PSF) with a dark region around the obscured star object. Electric field conjugation (EFC) is an iterative nonlinear optimization procedure that uses measurements of the electric field at the image to determine the DM displacements that modify the PSF to create the region of high contrast in the image. EFC requires a numerical model of the coronagraph to calculate the Jacobian of the system, which is used, along with regularization, to solve for the DM displacements for each iteration of the nonlinear optimization. Ideally, the coronagraph is aligned and calibrated, and the calibration data are used in the numerical model for calculating the Jacobian. However, calibration and alignment measurements always contain uncertainty resulting in calibration error. Therefore, the Jacobian calculated from the numerical model is not an exact representation of the physical coronagraph, and the resulting DM solution for an EFC iteration does not have the exact impact on the electric field of the coronagraph as predicted by the EFC. The result is slow convergence, and, as will be shown, the necessity of more restrictive regularization. Using Monte Carlo trials, we investigate the effect of calibration error on EFC convergence and regularization. Comparison to results from the High Contrast Imaging Testbed Hybrid Lyot Coronagraph are also presented.
David Marx, Byoung-Joon Seo, Brian Kern, Erkin Sidick, Bijan Nemati, and Ilya Poberezhskiy, "Electric field conjugation in the presence of model uncertainty," Proc. SPIE 10400, Techniques and Instrumentation for Detection of Exoplanets VIII, 104000P (Presented at SPIE Optical Engineering + Applications: August 09, 2017; Published: 1 September 2017); https://doi.org/10.1117/12.2274541.
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