Experimental results of Multi-Stage Four Quadrant Phase Mask Coronagraph

In the framework of exoplanet direct imaging, a few coronagraphs have been proposed to overcome the large flux ratio that exists between the star and its planet. However, there are very few solutions that gather in the same time broad band achromaticity, a small inner working angle (shortest angular distance for planet detection), a good throughput for the planet light, and a mature technical feasibility. Here, we propose to use a combination of chromatic Four Quadrant Phase Mask coronagraphs to achromatize the dephasing of this well-studied monochromatic coronagraph. After describing the principle of the technique, we present preliminary results for a compact prototype. Contrast larger than 10000 are reached with more than 250 nm of spectral bandwidth in the visible. Stability over time and effect of the filtering is also discussed.