Accueil du site > Equipes de Recherche > LIOA Lasers, Instrumentation Optique et Applications > Mesures et Instrumentation Optique – Optical Measurements and Instrumentation
par- 24 juin 2009
Contact : Hervé Gilles
Since 2003, LIOA team is involved in the area of optical instrumentation and in the development of advanced techniques for optical sensing. Two main research themes are currently under investigation.
This research topic is developped in the frame of a collaboration with Thales Air System (Limours, France). The goal of this project is to integrate optical sensors in the structure of large RADAR antennas. Their main functions is the measure the antenna mechanical deformations in order to maintain optimal performances after electronical compensations. Two different optical devices were developped so far. The first one consists in a laser plane parallel to the deformable surface, hence corresponding to a reference plane. The local deviation from this reference plane is measured by intercepting the laser plane with distributed sensors based on a bundle of optical fibers. Light coming out from the fibers is analysed using detectors such as PSD or CCD/CMOS which finally gives the deformation modes of the whole antenna. The second device uses the polarization state of the light over the reference laser plane to measure the transverse deviation.
During total reflection on a surface separating two dielectric media, the evanescent wave in the lower refractive index medium will induce a beam displacement of a fraction of the wavelength. LIOA group has developped a new technique for the measurement of these micro-displacements (Goos-Hänchen for longitudinal displacement and Imbert-Fedorov for transversal displacement). The experimental method for these measurements is based on the periodic polarization rotation of the incident beam followed by the detection of the spatial shift of the reflected beam using a PSD sensor. We have also studied displacement effects on a interface separating a dielectric medium and a metal. For a TM incident polarization state and a correct incident angle, it is possible to excite a plasmonic resonance mode on the interface. Using a gold layer with nanometric thickness deposited on a silica prism, we also observed a Goog-Hänchen shift which was strongly dependent on the nature of the dielectric medium.