Toward the stability required for direct observations of exoplanets with nulling interferometry

In the literature, one can find requirements for nulling IR interferometry in terms of nulling ratio nl and stability of this nulling ratio sigma(nl) for the observation of an exo-Earth in a 1AU orbit around a solar type star located at 10pc from the Earth: nl = 10(-5) between 7 and 20 mu m and sigma(nl) = 3 . 10(-9) over 10 days.(1) These requirements are very demanding. We report on studies made to obtain the technological requirements in terms of nulling ratio and stability of this nulling ratio as function of the targeted planets and stars. In addition we present methods of dithering developed for the NULLTIMATE test bench to achieve the maximum stability.