Learning by Research

Her Thesis Title: Polarimetry measurements and observations at millimeter wavelengths with KIDs

Scientific Context and Objectives

The polarization of electromagnetic radiation serves as a crucial information carrier for probing the physical processes of the Universe, ranging from galactic to cosmological scales. Its analysis allows for the mapping of magnetic fields within molecular clouds and the study of polarization modes in the Cosmic Microwave Background (CMB), which are vestiges of the primordial phases of the Universe. Detecting these often extremely weak signals imposes drastic constraints on detector sensitivity and the control of instrumental biases.

Technological Development: The LEKID Framework

The core of Sofia thesis is based on the use of LEKID (Lumped Element Kinetic Inductance Detector) type detectors, an innovative superconducting technology for millimeter-wave astronomy. The experimental approach covered the entire development chain:

• Design and Fabrication: Production of detectors in a cleanroom environment using architectures tailored to specific scientific objectives.
• Laboratory Characterization: Performance evaluation in a cryogenic environment using sky simulators to validate sensitivity and polarization response.
• Space Validation: The achieved performance levels were approved by the CNES, confirming that these detectors meet the requirements for future cosmological space missions.

Calibration and Instrumentation: The COSMOCal Project

To ensure the integrity of polarization measurements, a significant portion of Sofia’s research was dedicated to instrumental metrology and the development of reliable reference standards. Within this framework, a millimeter-wave reference source was designed and developed to simulate a fully polarized celestial signal, such as a quasar. This calibration system underwent rigorous laboratory validation before being integrated into an operational environment. Its coupling with the NIKA2 camera at the IRAM 30-meter telescope demonstrated its relevance for real-world observations by significantly improving the reliability of polarization angle measurements. This device is now intended for satellite deployment.

Scientific Application: Dynamics of the W43 Region

The implementation of these technological tools found direct application in the study of star formation processes. An observation campaign conducted with the NIKA2 instrument allowed for a detailed exploration of the W43 region, a particularly active site for massive star formation. Using the collected polarization data, the magnetic field structure was mapped with unprecedented precision to analyze its influence on gas dynamics. This work demonstrated, for the first time, that a more intense magnetic field is correlated with a higher fragmentation rate within molecular clouds.

Conclusion and Perspectives

Sofia’s work demonstrates the effectiveness of an integrated approach, linking fundamental instrumentation to astrophysical data analysis. Beyond the contribution to fundamental astrophysics, the developed detection technologies offer potential for transfer to other high-precision fields, such as medical imaging or new energy technologies.

Key words:  polarization, instrumentation, Kinetic Inductance Detectors