Abstract-2D and 3D Terahertz Imaging and X-Rays CT for Sigillography Study

• M. Fabre, 
• R. Durand, 
• L. Bassel, 
• B. Recur, 
• H. Balacey, 
• J. Bou Sleiman, 
• J.-B. Perraud, 
• P. Mounaix, 

http://link.springer.com/article/10.1007%2Fs10762-017-0356-3

Seals are part of our cultural heritage but the study of these objects is limited because of their fragility. Terahertz and X-Ray imaging are used to analyze a collection of wax seals from the fourteenth to eighteenth centuries. In this work, both techniques are compared in order to discuss their advantages and limits and their complementarity for conservation state study of the samples. Thanks to 3D analysis and reconstructions, defects and fractures are detected with an estimation of their depth position. The path from the parchment tongue inside the seals is also detected.

Abstract-Liquid index matching for 2D and 3D terahertz imaging

J. B. Perraud, J. Bou Sleiman, B. Recur, H. Balacey, F. Simoens, J. P. Guillet, and P. Mounaix

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-32-9185

Two-dimensional (2D) terahertz imaging and 3D visualization suffer from severe artifacts since an important part of the terahertz beam is reflected, diffracted, and refracted at each interface. These phenomena are due to refractive index mismatch and reflection in the case of non-orthogonal incidence. This paper proposes an experimental procedure that reduces these deleterious optical refraction effects for a cylinder and a prism made with polyethylene material. We inserted these samples in a low absorption liquid medium to match the sample index. We then replaced the surrounding air with a liquid with an optimized refractive index, with respect to the samples being studied. Using this approach we could more accurately recover the original sample shape by time-of-flight tomography.

© 2016 Optical Society of America

Full Article  |  PDF Article

Abstract-Low-frequency noise effect on terahertz tomography using thermal detectors

J. P. Guillet, B. Recur, H. Balacey, J. Bou Sleiman, F. Darracq, D. Lewis, and P. Mounaix
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-22-6758

In this paper, the impact of low-frequency noise on terahertz-computed tomography (THz-CT) is analyzed for several measurement configurations and pyroelectric detectors. We acquire real noise data from a continuous millimeter-wave tomographic scanner in order to figure out its impact on reconstructed images. Second, noise characteristics are quantified according to two distinct acquisition methods by (i) extrapolating from experimental acquisitions a sinogram for different noise backgrounds and (ii) reconstructing the corresponding spatial distributions in a slice using a CT reconstruction algorithm. Then we describe the low-frequency noise fingerprint and its influence on reconstructed images. Thanks to the observations, we demonstrate that some experimental choices can dramatically affect the 3D rendering of reconstructions. Thus, we propose some experimental methodologies optimizing the resulting quality and accuracy of the 3D reconstructions, with respect to the low-frequency noise characteristics observed during acquisitions.

© 2015 Optical Society of America

Full Article  |  PDF Article