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Abstract

From the birth of stars and planetary systems to the image of supermassive blackholes, the recent observations of astronomical objects at the highest angular resolution have profoundly changed our vision of our surrounding universe. In this field, aperture synthesis with Very Long Baseline interferometry (VLBI) and optical infrared interferometry are currently the two techniques that provide the highest angular resolution achievable. With its shorter wavelength, infrared interferometry, still confined at 100m scale baseline, could be envisioned as one of the most promising technique to go even further. The extension of this technique to a large number (N>15) of telescopes and kilometric baselines would represent a major step for observational astronomy, in particular for the study of nascent stars and forming planetary system. Nevertheless, such an infrastructure will also require major technological developments, with many challenges and cannot necessarily be extrapolated from current existing ones such as the Very Large Telescope Interferometer.

 
By its ease of operation in a practical infrastructure, heterodyne detection offers a complementary path to address the problem of kilometric baseline and aperture synthesis with a large number of telescopes. In the past, through the pioneer work of maser inventor and Nobel Prize C.H. Townes and his team, heterodyne detection was the first technique able to combine 2 telescopes in the mid-infrared and to obtain closure phases with 3 telescopes, on the Infrared Spatial Interferometer (ISI) in UC Berkeley. Routinely observing the sky during almost 20 years, ISI provided valuable scientific results well ahead of his time, anticipating the following generation of direct mid-infrared interferometric instruments e.g. MIDI and MATISSE. Despite these results, the limitations of heterodyne detection in terms of sensitivity have kept muting the relative advantages of this technique.

 
During the past few years, the breakthroughs in mid-IR detectors, laser synchronisation, microwave photonics, quantum optics and frequency combs, have though permanently pushed away the foremost limitations considered for heterodyne interferometry. In the light of these developements, and in the context of the rising of the mid-IR technologies, it appears that the previous limitations in terms of integration bandwidth and sensitivity, signal correlation and local oscillator synchronization, are now considerably modified.

 
Such progresses open a new way to envision aperture synthesis with heterodyne interferometry. From a 2020 perspective, this workshop aims at bringing together the forefront specialists of these different communities, to provide a comprehensive review of these current technologies, and to foresee the future and the exciting potential of an heterodyne instrument for astronomical aperture synthesis with kilometric baseline in the mid-infrared.

Joint organisers and support

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