2 sujets /DAp/LSIS

Dernière mise à jour : 18-06-2021


 

Study of Polarimetric Bolometer Arrays with Spectroscopic Capabilities for Astrophysics

SL-DRF-21-0652

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire des spectro-Imageurs spatiaux (LSIS)

Saclay

Contact :

Louis RODRIGUEZ

Vincent REVERET

Starting date : 01-10-2021

Contact :

Louis RODRIGUEZ
CEA - DRF/IRFU/DAP/LSIS

0169086948

Thesis supervisor :

Vincent REVERET
CEA - DSM/IRFU/DAp/LSIS

01 69 08 74 02

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.
Deep Learning and gamma spectroscopy: a new signal processing approach for CdTe detectors data analysis

SL-DRF-21-0316

Research field : Instrumentation
Location :

Direction d’Astrophysique (DAP)

Laboratoire des spectro-Imageurs spatiaux (LSIS)

Saclay

Contact :

Olivier LIMOUSIN

Starting date : 01-10-2021

Contact :

Olivier LIMOUSIN
CEA - DRF/IRFU/DAP/LSIS

01 64 50 15 03

Thesis supervisor :

Olivier LIMOUSIN
CEA - DRF/IRFU/DAP/LSIS

01 64 50 15 03

This thesis at the interface between nuclear instrumentation and applied mathematics consists in developing and implementing advanced methods for processing spectral data from CdTe Caliste detectors for high-energy photons. These sensors, resulting from fundamental research in space astrophysics, are the basic building block of the Spid-X gamma camera born from joint technological developments between the CEA and the company 3D PLUS. It aims at characterizing radiative environments in the framework of nuclear surveillance, for the safety of nuclear operations or research facilities, or for the dismantling of installations.

The methods studied will use Deep Learning tools with the objective of analyzing gamma spectra acquired in a complex environment inducing spectral distortions, potentially difficult to interpret with classical algorithms.



For this purpose, the PhD student will carry out the following lines of study:

- The identification of radioelements and the measurement of their proportion in the signal with one or several absorbing and scattering materials between the sources and the detector (methods: Monte-Carlo Geant4 simulations, Bayesian neural networks, confidence robust learning and experimentation).

- Determination of the nature of the material crossed and the thickness crossed (methods: adversarial neural networks (GANs), self-encoding, experimentation).

- The application to coded mask imaging methods. Depending on the results obtained in the two previous axes and the resulting discovery space, the methods may be applied to the theme of coded mask methods for gamma-ray imaging.

 

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