Abstract-Terahertz waves for contactless control and imaging in aeronautics industry

 

A. Chopard, J. Bou, Sleiman, Q. Cassara, J.P. Guillet, M. Pan, J.B. Perraud, A. Susset, P. Mounaix, 

https://www.sciencedirect.com/science/article/abs/pii/S0963869521000724

The usability of terahertz systems for specific inspection tasks and imaging in the aeronautics industry is assessed. Especially, we demonstrate the suitability of Frequency-modulated continuous-wave (FMCW) radars for health monitoring and see-through imaging. Additionally, terahertz time-domain data processing is performed for multi-layered paint structure characterization. FMCW radar principles are introduced. Available systems are described along with their benefits and limitations. Defect detection capabilities and progresses towards airplane covering see-through imaging are illustrated through FMCW experimental results on real samples. The suitability of FMCW radars as an advanced contactless non-destructive testing (NDT) tool for the aeronautics industry and maintenance services is demonstrated. A second application, based on terahertz time domain techniques, targets the characterisation of multi-layered painting structures through the assessment of dielectric properties and individual thickness of each layer deposited. Beside the review of extraction methods, the introduced new algorithm allows to derive a parametric transfer function, thus denoting the main contributions which give rise to the recorded terahertz electromagnetic field. Such a development pushes further the understanding and characterization of stratified structures by means of terahertz radiations and represents an indispensable tool to efficiently localise any deviation to the nominal painting stack in terms of thickness or dielectric properties.

Abstract-Shape-from-focus for real-time terahertz 3D imaging

J.-B. Perraud, J. P. Guillet, O. Redon, M. Hamdi, F. Simoens, and P. Mounaix

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-3-483

Thanks to significant advances in real-time terahertz imaging in terms of resolution and image quality, adapting and extending optical methods for 3D imaging at the millimeter scale is now promising. The shape-from-focus algorithm is a post-processing tool used in optical microscopy to reconstruct the external shape surface of a convex surface object. Images acquired at different distances from the object-side focal plane are implemented in this algorithm. We localize the best focus position in the stack of images for each pixel and then reconstruct the object in 3D due to the short depth of field. In this Letter, we propose an application of this algorithm in active and real-time terahertz imaging. We achieve the experimental reconstruction in 3D with a terahertz waves imaging system composed of a powerful source and a real-time terahertz camera.

Abstract-Shape-from-focus for real-time terahertz 3D imaging

J.-B. Perraud, J.-P. Guillet, O. Redon, M. Hamdi, F. Simoens, P. Mounaix,

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-3-483

Thanks to significant advances in real-time terahertz imaging in terms of resolution and image quality, adapting and extending optical methods for 3D imaging at the millimeter scale is now promising. The shape-from-focus algorithm is a post-processing tool used in optical microscopy to reconstruct the external shape surface of a convex surface object. Images acquired at different distances from the object-side focal plane are implemented in this algorithm. We localize the best focus position in the stack of images for each pixel and then reconstruct the object in 3D due to the short depth of field. In this Letter, we propose an application of this algorithm in active and real-time terahertz imaging. We achieve the experimental reconstruction in 3D with a terahertz waves imaging system composed of a powerful source and a real-time terahertz camera.

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-Art Painting Diagnostic Before Restoration with Terahertz and Millimeter Waves

Jean-Paul Guillet, M. Roux, K. Wang, X. Ma, F. Fauquet, H. Balacey, B. Recur, F. Darracq, P. Mounaix
http://link.springer.com/article/10.1007/s10762-017-0358-1

Art painting diagnostic is commonly performed using electromagnetic waves at wavelengths from terahertz to X-ray. These former techniques are essential in conservation and art history research, but they could be also very useful for restoring artwork. While most studies use time domain imaging technique, in this study, a painting has been investigated using both time domain imaging (TDI) and frequency-modulated continuous wave (FMCW) system in the millimeter frequency range. By applying these systems to a painting of the eighteenth century, we detect and analyze the structure of some defects. This study underlines the differences between FMCW and TDI. We present the advantages and disadvantages of each technique on a real artwork.

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

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Abstract-Bulk magnetic terahertz metamaterials based on dielectric microspheres

Bulk magnetic terahertz metamaterials based on dielectric microspheres 

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-16-18340

M. Šindler, C. Kadlec, F. Dominec, P. Kužel, C. Elissalde, A. Kassas, J. Lesseur, D. Bernard, P. Mounaix, and H. Němec

Rigid metamaterials were prepared by embedding TiO2 microspheres into polyethylene. These structures exhibit a series of Mie resonances where the lowest-frequency one is associated with a strong dispersion in the effective magnetic permeability. Using time-domain terahertz spectroscopy, we experimentally demonstrated the magnetic nature of the observed resonance. The presented approach shows a way for low-cost massive fabrication of mechanically stable terahertz metamaterials based on dielectric microresonators.

© 2016 Optical Society of America

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Abstract-Terahertz imaging and tomography as efficient instruments for testing polymer additive manufacturing objects

J. B. Perraud, A. F. Obaton, J. Bou-Sleiman, B. Recur, H. Balacey, F. Darracq, J. P. Guillet, and P. Mounaix
https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-13-3462

Additive manufacturing (AM) technology is not only used to make 3D objects but also for rapid prototyping. In industry and laboratories, quality controls for these objects are necessary though difficult to implement compared to classical methods of fabrication because the layer-by-layer printing allows for very complex object manufacturing that is unachievable with standard tools. Furthermore, AM can induce unknown or unexpected defects. Consequently, we demonstrate terahertz (THz) imaging as an innovative method for 2D inspection of polymer materials. Moreover, THz tomography may be considered as an alternative to x-ray tomography and cheaper 3D imaging for routine control. This paper proposes an experimental study of 3D polymer objects obtained by additive manufacturing techniques. This approach allows us to characterize defects and to control dimensions by volumetric measurements on 3D data reconstructed by tomography.

© 2016 Optical Society of America

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Abstract-Discrimination and identification of RDX/PETN explosives by chemometrics applied to terahertz time-domain spectral imaging

J. Bou-Sleiman, J.-B. Perraud, J.-P. Guillet, P. Mounaix

IMS, CNRS, Bordeaux Univ. (France)

B. Bousquet

CELIA, CNRS, Bordeaux Univ. (France)

N. Palka

Military Univ. of Technology (Poland)

Proc. SPIE 9651, Millimetre Wave and Terahertz Sensors and Technology VIII, 965109 (October 21, 2015); doi:10.1117/12.2197442

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2466618

Detection of explosives has always been a priority for homeland security. Jointly, terahertz spectroscopy and imaging are emerging and promising candidates as contactless and safe systems. In this work, we treated data resulting from hyperspectral imaging obtained by THz-time domain spectroscopy, with chemometric tools. We found efficient identification and sorting of targeted explosives in the case of pure and mixture samples. In this aim, we applied to images Principal Component Analysis (PCA) to discriminate between RDX, PETN and mixtures of the two materials, using the absorbance as the key-parameter. Then we applied Partial Least Squares-Discriminant Analysis (PLS-DA) to each pixel of the hyperspectral images to sort the explosives into different classes. The results clearly show successful identification and categorization of the explosives under study.
 © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

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

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Abstract-Review of Terahertz Tomography Techniques

• J. P. Guillet, 
• B. Recur, 
• L. Frederique, 
• B. Bousquet, 
• L. Canioni, 
• I Manek-Hönninger, 
• P. Desbarats, 
• P.

Mounaix

http://link.springer.com/article/10.1007%2Fs10762-014-0057-0

Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.

Abstract-Ultrafast carrier response of Br+-irradiated In0.53Ga0.47As excited at telecommunication wavelengths

L. Fekete¹, H. Němec¹, Z. Mics¹, F. Kadlec¹, P. Kužel^1,a), V. Novák², J. Lorinčík^3,4, M. Martin⁵, J. Mangeney⁵, J. C. Delagnes⁶ and P. Mounaix⁶
^{http://scitation.aip.org/content/aip/journal/jap/111/9/10.1063/1.4709441}

1 Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
2 Institute of Physics ASCR, Cukrovarnická 10, 162 53 Prague 6, Czech Republic
3 Institute of Photonics and Electronics ASCR, Chaberská 57, 18251 Prague 8, Czech Republic
4 Department of Physics, Faculty of Science, J.E. Purkinje University, Ceske mladeze 8, 40096, Usti nad Labem, Czech Republic
5 Institut d’Electronique Fondamentale, Université Paris XI, UMR CNRS 8622, 91405 Orsay Cedex, France
6 Laboratoire Ondes et Matière d’Aquitaine, Université Bordeaux I, UMR CNRS 5798, 351 Cours de la Libération, 33405 Talence Cedex, France
View the Scitation page for Institute of Physics AS CR (IOP).
View the Scitation page for JE Purkyn? University.
View the Scitation page for University of Bordeaux.
View the Scitation page for University of Paris-Sud.
a) E-mail: kuzelp@fzu.cz.
J. Appl. Phys. 111, 093721 (2012); http://dx.doi.org/10.1063/1.4709441

We present results of infrared pump—terahertz probe experiments applied to a set of In_0.53Ga_0.47As films irradiated with heavy ions (Br⁺) at doses from 10⁹ to 10¹²cm⁻².Photoexcitation at 1400 nm (0.89 eV) allowed us to characterize the response close to telecommunications’ wavelengths whilst avoiding the intervalley carrier scattering observed when a shorter wavelength excitation is used. The excitation fluence was varied in our experiments in order to characterize the dynamics in detail: the lifetimes and mobilities of both electrons and holes were retrieved, and the trap filling and carrier diffusion were clearly observed. The In_0.53Ga_0.47As film irradiated by the dose of 10¹²cm⁻² exhibits simultaneously ultrashort electronlifetime (∼300 fs) and very high electron mobility (2800 cm²V⁻¹s⁻¹). These findings are particularly important for the design of terahertz emitters controlled by lasers operating at standard telecommunication wavelengths.

Abstract-Broadband effective magnetic response of inorganic dielectric resonator-based metamaterial for microwave applications

• R. Yahiaoui, 
• U.-C. Chung, 
• S. N. Burokur, 
• A. de Lustrac, 
• C. Elissalde, 
• M. Maglione, 
• V. Vigneras, 
• P. Mounaix

http://link.springer.com/article/10.1007/s00339-013-8033-4

A single-sized dielectric cylinder-based metamaterial is fabricated from TiO₂ nanoparticles, using a bottom-up approach. The sub-elements constituting the metalayer are embedded in a nonmagnetic transparent host matrix in the microwave regime and arranged in a square lattice. We demonstrate numerically and experimentally a broadband magnetic activity. The key feature to achieve this performance remains in the high aspect ratio of the metamaterial building blocks. This is a very promising step towards complex electromagnetic functions, involving low-cost metamaterials with simple fabrication.