Improving the broadband contrast at small inner working angles using image sharpening techniques

The detection of extrasolar planets, using both space- and ground-based telescopes, is one of the most exciting fields in astronomy today. From the ground, the upcoming Extremely Large Telescopes will offer a significant increase in our capability to directly image exoplanets and could potentially lead to the direct detection of planets in the habitable zone. To obtain contrasts better than 10^-7-10^-9 requires precise wavefront control algorithms. Although wavefront control techniques, such as Electric Field Conjugation, stroke minimization and speckle nulling, have been already developed and will soon be operational on 8-m class telescopes, they primarily function in monochromatic light and at moderate separations (r>3 λ=D). While wavefront control simulations combining polychromatic light and smaller inner working angles (1.2 λ=D for example) have shown promising results, experimental verification is still ongoing. In this paper, we discuss the challenges emerging when pushing the limits of high-contrast imaging and present our latest contrast results using wavefront control techniques optimized for small separations. This work is performed using the NASA Ames Coronagraph Experiment (ACE) laboratory testbed located in California.