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Direct imaging is crucial to increase our knowledge on extrasolar planetary systems. It can detect long orbits planets that are inaccessible by other methods and it allows the spectroscopic characterization of exoplanet’s athmospheres. During the past fewyears, several giant planetswere detected by direct imaging methods. Yet, as exoplanets are 103 to 1010 fainter than their host star in visible and near-infrared wavelengths, direct imaging requires extremely high contrast imaging techniques, especially to detect low-mass and mature exoplanets. Coronagraphs are used to reject the diffracted light of an observed star and obtain images of its circumstellar environment. Nevertheless, coronagraphs are efficient only if the wavefront is flat because aberrated wavefronts induce speckles in the focal plane which mask exoplanet images. Thus, wavefront sensors associated to deformable mirrors are mandatory to correct speckles by reducing aberrations. To test coronagraph techniques and focal plane wavefront sensors at very high contrast level, we developed the THD2 bench in the optical wavelengths. On the THD2 bench, we routinely reach 108 raw contrast level inside the dark hole over broadbands but this level is not sufficient to detect low-mass exoplanets. At this level, it seems that many experimental factors can affect the contrast and understanding which one is limiting the final detection contrast will be useful to upgrade the THD2 bench and to develop the next generation of space-based instruments (LUVOIR, HabEx) aiming to reach 10-10 contrast level. We started a complete study of the instrumental limitations of the THD2 bench, focusing on scattering which could add intensity on the detector or polarization effects and residual laboratory turbulences. In this paper, we present the methods used to estimate the amount of scattered light that reaches the final detector on the THD2 bench.
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