Two new proposals for high resolution imaging in astronomy: Parametric interferometers and temporal hypertelescopes
Résumé
High resolution stellar interferometers are very powerful and efficient instruments to get a better knowledge of our Universe through direct imaging or spatial coherence. Many important results are currently obtained with interferometers such as Keck telescopes or VLTI. For 30 years, we have developed at Limoges lab a set of new techniques to simplify the architecture of a telescope array dedicated to high resolution imaging. In a first step, I will present you a tutorial on the current status of high resolution imaging techniques mainly based on the coherence analysis. Second, I will explain how we intend to use non-linear optics in this field. Our team proposes to explore the possibility of using non-linear optical techniques to avoid lots of technical difficulties related to infrared optics (components transmission, thermal noises, thermal cooling,...). This is a promising alternative technique for the detection of infrared optical signals. Indeed, we have experimentally demonstrated that sum frequency generation in a non-linear crystal (PPLN) does not result in an additional bias on the interferometric data provided by a stellar interferometer up to the photon counting regime. Last, I will describe a new kind of instrument allowing to provide direct images. The temporal hypertelescope is a new version of spatial hypertelescope proposed by A. Labeyrie. Our temporal version simplifies the implementation through a transposition from the spatial to the temporal domain. The experimental demonstration has been achieved with an 8-telescope laboratory prototype. A servo-control system has been implemented using a genetic algorithm and a phase diversity technique allowing to reach a $10^3-10^4$ dynamics. At the present time, we are studying noise limits up to the photon counting regime.