07 Décembre – Thesis defense - Adrien Chopard

10 h Amphi Jean-Paul Dom - Laboratory IMS / Building A31 (University of Bordeaux - Talence campus)

Terahertz inspection through FMCW radar developments and advanced imaging approaches.

Following recent developments of systems performances in the terahertz spectral range, this work reports on several instrumentation advances, intended as complementary tools for contactless Non-Destructive Testing. On the field of continuous wave sensing, even though optimal for the recovery of terahertz representations, standard single point focused imaging features an intrinsic recording time limitation. As an alternative, a transposition toward real-time imaging was undertaken. The development of a versatile galvanometric illumination process ensured the mitigation of intrinsic restraining factors in such a geometry. It ultimately led to reliable full-field imaging, up to the demonstration of enhanced real-time 3D tomographic inspection capabilities. Subsequently, the use of coherent sensing, through the detailed development of a FMCW (Frequency Modulated Continuous Wave) radar transceiver, operating in the 150 GHz frequency range, demonstrated nominal longitudinal sensing performances, based on a homodyne harmonic mixing scheme. Namely, the application of a normalization deconvolution procedure, along with a Phase Locked Loop stabilized architecture, ensures its reliable and consistent operation with high dynamic range measurement capabilities up to 100 dB and raw measurement rates up to 7.62 kHz. Those developments naturally led to applicative considerations with targeted Non-Destructive Testing oriented problematics. Namely, in parallel of volumetric inspection and specific instrumentation advances, the sensing capabilities for constactless thickness extraction on millimetric stratified sample geometries was obtained. Ultimately, with similar thickness and topological inspection aspirations, coherent wave front sensing, through lensless focused imaging, was explored. It called on multi-plane phase retrieval and off-axis holography approaches, through single point sensing in the sub-terahertz range, and further transposed at 2.5 THz, with real-time recording.

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