The hypertelescope at work with a BIGRE integral field unit

ABSTRACT Dense Aperture Masking (DAM) is a high-contrast imaging technique which enhances the capabilities of the current direct imaging instrumentation, mainly to detect low bright companions at small separation from their parent star. DAM benefits from the experience achieved with the integral field unit installed on SPHERE spectrograph at the VLT (BIGRE, Antichi et al. 2009) with a very similar optical design. More in detail, it is obtained by exploiting the BIGRE integral field unit - composed of two consecutive micro-lens arrays - to subdivide the telescope pupil in many sub-pupils, preserving their relative positio n and providing the same amount of spatial f iltering to each one. We present here results of a system study we pursued for a proficient implementation of BIGRE-DAM. We focus on the case of an 8 m class telescope coupled with the instrument NACO at the VLT. We detail on how the optical design and the related mechanical implementati on of a DAM unit could be successfully achieved within NACO thanks to a wise optimization of the BIGRE micro-lenses array, adopted as sub-pupils re-imager instead of integral field unit. Diffraction limit is achieved by optical design and good apochromatic performan ces are proven for a narrow-b and filter around 2.18 micron. Keywords: imaging interferometry, integr al field unit, optical design