Focal Plane Wavefront Sensing with a self-coherent camera

Characterization of exoplanets with long orbital periods requires direct ima ging which is challenging. The objective is the suppression of the light of the star that is 1 04 to 1010 times brighter than its planet which is at less than 1 arcsec. Coronagraphs were propo sed to suppress the stellar light but their performance is strongly limited by wavefront aberrations that induce s tellar speckles in the science image. Adaptive optics correct for most of the atmospheric turbulence but quasi-static aberrations still remain because of flexures with pointing, optical aberrations of moving optic s, and so on. Classical adaptive optics cannot calibrate the quasi-statics because of di fferential aberrations between the science image and the wavefront sensing image. Since 2006, our team works on a s elf-coherent camera (SCC) that estimates both phase and amplitude aberrations from the science image. Th e SCC creates a reference beam that interferes with the speckles in a Fizeau scheme and spatially modulates them in the science image. Demodulating the signal, we retrieve the complex amplitude of the electric field in the science image and use a deformable mirror to enhance the contrast in a dark hole. We obtained contrasts as high as 108 between 4 and 15 λ/D in laboratory but chromatism may be an issue working with large bandwidths. In this paper, we present a new version of the SCC that may o vercome this limitation. We ran preliminary numerical simulations and obtained preliminary laboratory resu lts.