An important instrumental project in the context of high angular resolution observations of faint objects (cf. exo-zodi, exo-planets) located very near a bright point-like source (cf. the host star) has been carried out at IAGL. This research has been mainly focused on the pre-phase A design of the Ground-based European Nulling Interferometer Experiment (GENIE), in collaboration with the European Space Agency and the European Southern Observatory. A software has been built to simulate future GENIE observations, taking into account all noise sources including the effect of atmospheric turbulence and thermal background emission. The control of OPD, dispersion and intensity are very critical for the operation of a ground-based nulling interferometer, and has been tackled thoroughly. Advanced chopping methods have also been investigated. In the context of GENIE, several research projects are under development. One of these is the subject of the PhD thesis of O. Absil. It concerns the detection of circumstellar dust clouds, especially around Vega-type stars and Young Stellar Objects. Besides GENIE, work on the optimization of the aperture configurations for the DARWIN interferometer has also been continued at IAGL.

       As of 1st January 2004, IAGL is a member of the European Interferometry Initiatives (EII, OPTICON) in the context of the 6th Framework Program. Among the planned activities of the Optical Interferometry Network of the European Interferometry Initiatives, Workpackage 3 coordinated by IAGL directly aims at developing the vision for a next-generation interferometric facility. Some funds have also been made available to study the problem related to the mass production of telescope units.

       Additional activities in the field of high angular resolution astrophysics also involve the study of innovating Achromatic Phase Shifters (PhD work of D. Mawet). The latter are mandatory components in the field of nulling interferometry (cf. GENIE) and phase coronagraphy. Indeed, in order to detect faint objects (cf. exo-planets, for instance) around a central bright target (cf. host star), one must attenuate it by all means. To do this, the most efficient way is to "create" a destructive interference on the light coming from the blinding star. This technique is known as "nulling" and is common to the two fields mentioned above; the first with several telescopes, the second with only one aperture. How does it work? The incoming light from the central object is divided in several beams over which one applies a differential phase shift. This operation result in changing the sign of, for instance, one of the two beams by means of a so-called phase shifter. Then, when we properly recombine the separate beams together, they simply subtract from each other! Achromatic means that we can apply this process over a large spectral bandwidth (range of colours). This quality is required for the detection and characterisation of exo-planets. Innovating APSs consist of subwavelength structures, i.e. imprinted on a scale smaller than the wavelength of the incident light (1/10 microns for the infrared for instance). These structures are seen by the incident light as a homogeneous medium with very specific and amazing properties one can play with to design flexible APSs. The implementation on interferometers (DARWIN) and coronagraphs (Four Quadrant Coronagraph) of such components is under study by our team. Some success has already been encountered. Indeed, the first Achromatic Four Quadrant Phase Mask will soon be tested. The latter is not composed of subwavelength structure which are very costly but directly profits from recent researches on this subject.

Web pages:Sandrine Sohy
Last modification: June 7, 2004