Experimental results with a second-generation Roddier & Roddier phase mask coronagraph

Abstract

Context: Coronagraphic techniques are required to observe substellar mass companions close to nearby bright stars by direct imagery. Phase mask coronagraphs are particularly interesting because they give access to the innermost regions.While the principle of the first such concept was validated experimentally a decade ago, the achieved brightness attenuation was too low to be conclusive, probably due to the imperfect thickness profile of the mask. Aims: We have manufactured and tested a second-generation Roddier & Roddier coronagraph in preparation for the development of more elaborate phase mask designs, planned to be used in the future European Extremely Large Telescope. Methods: Amonolithic phase mask was made by ion beam machining. Experimentally obtained coronagraphic images were compared with simulated images. Results: Good agreement with theory was obtained. A peak attenuation of 216 was achieved, and a contrast of ∼10-5 was measured at 5.7 λ/D. The results exploring contrasts obtained at different distances from the star for different mask dimensions are particularly interesting, confirming predictions made in the literature. © 2010 ESO.