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Abstract: We propose to use a Mach–Zehnder interferometer to make achromatic the four quadrants phase mask coronagraph. The interferometer is used to get the achromatic π phase term. Two complementary binary masks of transmission 1 and 0 for quadrants of the same parity are set in the focal plane formed inside the interferometer. There is an equipartition of the energy in the exit aperture images, one being similar to the entrance aperture, the other being coronagraphied. We present preliminary results obtained with a coherent light. The current throughput of the experiment is 25% only, but we give indications on how to improve it. To cite this article: C. Aime et al., C. R. Physique 8 (2007). [Copyright &y& Elsevier]