05 Novembre – Thesis defense - Jean-Baptiste Perraud

14 h15 Amphi Jean-Paul Dom / Laboratory IMS - building A31 (Talence)

Fast 3D terahertz imaging.

The aim of this work is to position terahertz imaging as a new tool dedicated to metrology and non-destructive testing. Its astonishing properties of both high penetration in dielectric materials and wavelength millimeter or even submillimetric make it a very exciting tool for applications such as non-destructive testing (NDT).
First, we presented two imaging techniques: one to move the object, point by point, in a focused terahertz beam to reconstruct, pixel by pixel, a two-dimensional image. The other technique is based on the use of a lens and a matrix sensor in the state of the art operating at room temperature. Thus we have imaged objects of interest, without mechanical displacement. Although this last technique is much faster than point-by-point imaging, the quality of the images obtained is not comparable and this because of two drawbacks. Thus, part of the work consists in the study of lighting strategies to limit the interferential optical effects induced by the coherence of the source. In addition, by deploying simulations of the entire optical chain with Zemax software, numerous quality images make it possible to consider applications in 2D (metrology, NDT) and 3D imaging. Thus, two complementary tomographic reconstruction techniques are tested on images obtained in real time; a technique inspired by X-ray imaging and a technique used in 3D optical microscopy that exploits the reduced depth of field of the lens. Finally, several spectroscopic and metrological studies are carried out in order to evaluate the behavior of the materials and the dimension of the objects starting from their THz images in 2D or with their 3D tomographic reconstruction. The work done is the foundation for deploying terahertz imagery to the application domain with unmatched image quality and real-time acquisition time.

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