The technique of pupil densification bridges the gap existing betweenconventionnal optical astronomy observing techniques and opticalinterferometry: it indeed leads to the concept of hypertelescope: an instrument that can provide direct images at the focus of an interferometer.The hypertelescope is the open sesame for high dynamic imaging with aninterferometer: indeed, the elementary remapping of the pupil operated by adensifier not only maximizes the dynamic range and the signal to noise ratioof images but also makes the interferometer compatible with most existingcoronagraphic devices.Moreover, a careful discussion about field of view show that for a dilutedarray, the pupil densification preserves all the relevant high angular resolution information collected by the interferometer and therefore inducesno field loss.

AMBER is the near I.R. focal instrument of the VLTI. It recombines 3 beams simultaneously and has spectral resolution capability allowing simultaneous spectrum, visibilities, differential visibilities, closure phase and differential phases measurements on the observed sources. We present here the general formalism used on AMBER in order to compute differential phases and differential visibilities, in complement to the article of Tatulli et al. (2006). We show that these differential observables have precisions close to the fundamental noises and we present an illustration of model-fitting using them on the binary star γ2 Velorum where we made a precise measurment of the astrometry of the 2 components (3.65±0.1 mas). 


One major technical hurdle that has to date been neglected in optical interferometry is measurement of polarization of light. However, thanks to pioneering works in the last decade, the interest of adding a polarimetric equipment has now been recognized. In this paper, I present a short overview of the astrophysical opportunities offered by optical polar-interferometry, but also a historical review of the already achieved instrumental steps.