The aim of this report is to present potential interest of development of our imaging terahertz systems as a safe, contact free and on-site non-destructive testing systems. These systems could be easly integrated in industrial facilities allowing the detection of surface, subsurface and in-depth defects in a variety of composite materials used in aeronautics. Our optical setups are based on the use of High-Electron-Mobility transistors (HEMT) as compact sensitive and rapid detectors operating at room temperature. The physical bases that explain the functioning of these sensors will be discussed. Our imaging systems and results of some case studies will be presented. L’objectif de ce travail est de présenter une nouvelle technologie de capteur de mesure du rayonnement térahertz et son application à des systèmes d'imagerie térahertz pour le contrôle volumique, non destructif, non nocif, sans contact et temps réel des matériaux diélectriques. Ces systèmes pourront être facilement intégrés dans des installations industrielles permettant la détection des défauts en surface, en sub-surface et en profondeur dans une large variété de matériaux composites par exemple. Nos configurations optiques sont basées sur l'utilisation de transistors à haute mobilité d'électrons (HEMT) comme des détecteurs compacts sensibles et rapides fonctionnant à la température ambiante. Les bases physiques qui expliquent le fonctionnement de ces capteurs seront discutées. Nos systèmes d’imagerie et les résultats de certains cas d’étude seront présentés. Introduction Parmi les technologies de contrôle non destructif (CND) des matériaux, on peut distinguer deux grandes catégories : les techniques surfaciques et les techniques volumiques. Pour cette dernière, les technologies les plus répandues dans les domaines électromagnétique et acoustique sont les rayons X, les ultrasons et l’infrarouge. Un nouveau domaine d’ondes électromagnétiques, les rayons T (Térahertz) est en train d’émerger. Ces ondes ont une fréquence et une longueur d’onde comprises respectivement entre 0,1 THz et 30 THz et 0,01 mm et 3mm. La bande térahertz représente ainsi la frontière entre deux domaines physiques : l’électronique pour les micro-ondes d’un côté et l’optique pour l’infra-rouge de l’autre. Journées scientifiques 24/25 mars 2015 URSI-France

We report on Terahertz wireless communications and fast imaging experiments at 300 GHz, using nanometer-sized transistors as detectors. The physical mechanism of the detection is related to the overdamped plasma waves in the transistor channel.

In this work we review the most important results concerning the physics and applications of FETs as Terahertz detectors. We present two experiments showing: i) Terahertz detection based on low cost 130 nm silicon technology Field Effect Transistors in the sub-THz range (0.2 THz up to 1.1 THz) and ii) first results on detection by FETs of emission from 3.1 THz Quantum Cascade Lasers.

We report on the resonant detection of a 3.1 THz radiation produced by a quantum cascade laser using a 250 nm gate length GaAs/AlGaAs field effect transistor at liquid nitrogen temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel. The detection is enhanced by increasing the drain current and driving the transistor into saturation regime. These results clearly show that plasma wave nanometer-size transistors can be used as detectors in all-solid-state terahertz systems where quantum cascade lasers act as sources.

We present a Terahertz (THz) p-Ge laser operating in a cyclotron resonance (CR) mode. Thanks to the use of the optimum crystallographic orientation of p-Ge with respect to crossed E⊥B fields, the laser line frequency is continuously tunable in the range 1.2–2.8 THz (40–90 cm−1) with the linewidth being 6 GHz (0.2 cm−1). We also show that due to such a wide CR radiation range, the laser can serve as a base for a THz spectrometer.

The mechanical properties of various inorganic organic films were studied and compared in order to investigate the relation between structural modifications and the mechanical behavior. Films were prepared by a sol–gel process and spin-coated on silicon substrate. The organic–inorganic hybrid is composed of a mixture of colloidal silica and organosiloxane precursors. The functionality of the organosiloxane and the nature of its organic part have been modified to obtain a structural change. Mechanical properties were studied using nanoindentation. Analysis of the strength evolution as a function of depth of indentation shows the layer hardness and elastic modulus. Moreover, coating and interface toughness and residual stresses were determined by a time resolved study of energy dissipation during indentation. The structural changes were determined using liquid and solid 29 Si NMR spectroscopy. Quantity of partially and fully condensed species in the deposited sol and final solid are discussed in relation to the mechanical properties.