Improving image contrast for the direct detection of exoplanets at small inner working angles

The detection of extrasolar planets, using both space- and ground-based telescopes, is one of the most exciting fields in astronomy today, with the ultimate goal of the direct direction of earth-like planets in the habitable zone. It is with this vision that the explorer mission EXCEDE selected by NASA for technology development, is designed. EXCEDE (Exoplanetary Circumstellar Environment and Disk Explorer) is composed of a 0.7 m telescope equipped with a Phase-Induced Amplitude Apodization Coronagraph (PIAA-C) and a 2000-element MEMS deformable mirror, capable of raw contrasts of 10-6 at 1.2 λ/D and 10-7 above 2 λ/D. Obtaining these contrasts requires precise wavefront control algorithms used in conjuncture with deformable mirrors. Unlike other optical systems, where the goal is to obtain the best wavefront, we aim at canceling the diffracted light coming from the parent star in a specific region to increase signal-to-noise of the planet. To do so, we use wavefront control techniques, such as Electric Field Conjugation (EFC) and speckle nulling, already developed and soon to be operational on 8-m class telescopes. One caveat is that the demonstration was done at moderate separations (r> 3λ/D).In this paper, we present tricks and techniques to perform high-contrast imaging at 1.2 λ/d using the NASA Ames Coronagraph Experiment testbed.