Demonstration of symmetric dark holes using two deformable mirrors at the high-contrast imaging testbed

The High Contrast Imaging Laboratory (HCIL) at Princeton has developed several important algorithms and technologies for space-based coronagraphy missions to detect earth-like exoplanets. Before June 2013 the HCIL was the only facility with two deformable mirrors (DMs) in series for focal plane wavefront control, which allows for quasi-static speckle correction on both sides of the image plane. From June through August 2013, the High-Contrast Imaging Testbed (HCIT) at JPL had a second DM installed. In this paper we report on the results of our Technology Development for Exoplanet Missions project to achieve high contrast in two symmetric dark holes using a shaped pupil (SP) coronagraph at the HCIT. Our previous experiment with a similar SP at the HCIT in 2007 yielded single-sided dark holes. That experiment utilized an iterative, batch-process wavefront estimator and Electric Field Conjugation for wavefront control. Our current tests use the faster Kalman filter estimator and the stroke minimization control algorithm. We use the same ripple-style SPs as in the previous HCIT experiment because that mask manufacturing technique proved successful. Our tests of symmetric dark holes in monochromatic light at the HCIT demonstrate Princeton's steady improvements in wavefront control and estimation techniques for a space-based coronagraphy mission.