Laboratory link : http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=2755
The Herschel Space Observatory, launched in 2009, has revolutionized our vision of the "Cold Universe". In particular, it has radically changed our understanding of star formation by highlighting the ubiquitous filamentary structures of gas and dust and their essential role in the very early stages of star formation.
On the other hand, the observations of the Planck satellite (also launched in 2009) in polarimetric mode have highlighted the presence of magnetic fields on large scales in molecular clouds. In these regions, the filaments can be either parallel to the magnetic field (low density filaments) or perpendicular (very dense filaments). But many questions remain.
In order to understand the set of physical processes implemented in these stellar formation zones and to explain the links with the complex structure of the surrounding interstellar medium (ISM), new extremely sensitive instruments must be developed in the submillimeter domain. It seems necessary, on the one hand, to be able to finely characterize the magnetic field (via the detection of polarized light) in several spectral bands and, on the other hand, to detect the presence of several tracers of the ISM via the emission of certain spectral lines (C+ at 158 µm in particular). These observations, made from space or aboard stratospheric balloons, strongly constrain the volume and mass of the on-board charge. The idea of gathering one or more light analysis functions within a compact detector is a step in this direction.
In this context, CEA has been developing for a few years now ultra-sensitive submillimeter bolometer arrays, capable of measuring the polarization within pixels, without the help of external polarizers. Developed in close collaboration with CEA-LETI in the framework of the B-BOP instrument on the SPICA observatory, this technology is in line with the developments of the Herschel-PACS detectors. These bolometers are developed in the framework of Labex Focus, 2 R&T CNES and ESA funding.
In 2019, a thesis defended at the laboratory demonstrated that it was possible to add spectroscopic capacity to these new generation arrays by coupling the detector arrays to a compact Fabry-Perot interferometric system. The experimental demonstration of the complete device remains to be done and this is the core of this thesis topic: to study, implement and characterize experimentally the scientific performances of this compact spectro-imager-polarimeter.
The first step will be to experimentally validate in a cryostat the Fabry-Perot mirror displacement system and to deduce its technical limitations. The second phase will consist in coupling this system to the bolometer arrays in order to produce and characterize the first prototypes of this new type of detectors. Finally, in a third part, the data processing aspect will be studied in order to extract the scientific signal as well as possible and to propose an adequate calibration.
This work may also pave the way to more applied applications in medical imaging or in the field of security controls in the TeraHertz band, as proposed by LETI with its developments of room temperature micro-bolometers.