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Courreges F.,Xlim Institute | Absi J.,University of Limoges | Laribi M.A.,University of Poitiers | Arsicault M.,University of Poitiers | Zeghloul S.,University of Poitiers
Proceeding - 2015 IEEE International Conference on Industrial Informatics, INDIN 2015 | Year: 2015

The aim of this work is to improve the safety and control robustness of robots interacting physically with humans by enhancing their contact perception. More specifically in the abdominal area, respiratory motions are clearly influencing the contact dynamics but have not yet been accounted for in the estimation of the contact impedance. We propose here a combined mechanical-respiratory model of impedance along with its on-line identification. Numerical and practical experiments with living subjects validate the identification process and show the relevance in accuracy of accounting for the respiratory beats. © 2015 IEEE.

News Article | February 15, 2017

Fig. 1: On the macroscopic scale, the pump light transforms into forward-propagating Stokes (FS) radiation, which is partially reflected from the fibre end and becomes backward-propagating Stokes radiation (BS) which is also amplified by the pump. In the region where both FS and BS are strong, they form interference pattern of standing wave, which is shown on the microscopic scale. In the low-field regions (denoted by red-color molecules) the molecules are in the ground state and strongly trapped, as shown by the potential in the bottom panel. Exactly these trapped molecules are Raman-active, leading to line narrowing. Credit: Forschungsverbund Berlin e.V. (FVB) Decreasing the emission linewidth from a molecule is one of the key aims in precision spectroscopy. One approach is based on cooling molecules to near absolute zero. An alternative way is to localize the molecules on subwavelength scale. A novel approach in this direction uses a standing wave in a gas-filled hollow fibre. It creates an array of deep, nanometer-scale traps for Raman-active molecules, resulting in linewidth narrowing by a factor of 10 000. The radiation emitted by atoms and molecules is usually spectrally broadened due to the motion of the emitters, which results in the Doppler effect. Overcoming this broadening is a difficult task, in particular for molecules. One possibility to overcome the molecular motion is by building deep potential traps with small dimensions. Previously, this was done e.g. by arranging several counterpropagating beams in a complicated setup, with limited success. In a cooperation effort of the Max Born Institute (A. Husakou) and Xlim Institute in Limoges, researchers show that subwavelength localization and line narrowing is possible in a very simple arrangement due to self-organization of Raman gas (molecular hydrogen) in a hollow photonic crystal fibre. Due to Raman scattering, the continuous-wave pump light transforms into the so-called Stokes sideband, which travels back and forth in the fibre due to reflections from fibre ends and forms a stationary interference pattern - a standing wave with interchanging regions of high and low field [Fig. 1]. In the high-field regions, the Raman transition is saturated and is not active, and the molecules have high potential energy since they are partially in the excited state. In the low-field region, the molecules are Raman-active, and they have low potential energy since they are close to the ground state. These low-field regions form an array of roughly 40 000 narrow, strong traps, which contain localized Raman-active molecules. The size of these traps is around 100 nm (1 nm = 10-9 m), which is much smaller than the light wavelength of 1130 nm. Therefore the emitted Stokes sidebands have a very narrow spectral width of only 15 kHz - this is 10 000 times narrower than the Doppler-broadened sidebands for the same conditions! The self-organization of the gas manifests also on the macroscopic scale. First, the calculations show that the Raman process mainly happens exactly in the fibre section where the standing wave is formed, as shown in the top panel of Fig. 1. Second, the macroscopic gradient of the potential leads to the gas flow towards the fibre end, which is observed by eye in the experiment. This strong localization and the linewidth narrowing can find various uses, e.g. in spectroscopy. However, it can also be used as well as a method to periodically modulate the density of the gas, which is naturally suited for developing quasi-phase-matching schemes for other nonlinear processes, such as effective generation of high harmonics. Explore further: Silicon nanoparticles pave the way toward nanoscale light emitters More information: M. Alharbi et al. Raman gas self-organizing into deep nano-trap lattice, Nature Communications (2016). DOI: 10.1038/ncomms12779

Tombelaine V.,Institute of Photonic Technologies Jena | Bergner G.,Institute of Photonic Technologies Jena | Vater E.,Institute of Photonic Technologies Jena | Schlucker S.,University of Osnabrück | And 6 more authors.
Optics Communications | Year: 2011

Supercontinuum fiber light sources with their extremely wide wavelength spectrum can provide new options for achieving specific wavelength distributions in a very flexible way. Two concepts for the combination of such supercontinuum light sources with a spectrally dispersive optical system and an interactive filter for modulating the light spectrum are discussed. These concepts provide the possibility to achieve laser-like light sources with an almost arbitrary shape of the spectrum, great flexibility in interactive tuning of the spectral properties and covering wavelengths from UV to the infrared range. © 2010 Elsevier B.V. All rights reserved.

Bui N.,XLIM Institute | Guiffaut C.,XLIM Institute | Reineix A.,XLIM Institute | Pouliguen P.H.,Directorate General of Armaments
IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) | Year: 2015

In this paper, we propose a FDTD(2,4) scheme to reduce numerical dispersion compared to the standard Yee scheme. This scheme is designed to retain a two dimensional stencil in the field update equations. We derive the numerical dispersion equation of this scheme and show its high-phase accuracy at low-grid resolutions. Moreover, the Courant-Friedrichs-Lewy condition (CFL) of this scheme does not decrease the usual standard time-step given by the CFL condition of the Yee scheme. With this scheme, we can model large structures with high accuracy results. © 2015 IEEE.

Labruyere A.,Xlim Institute | Jaffres L.,Xlim Institute | Jaffres L.,Horus laser S.A.S. | Couderc V.,Xlim Institute
Laser Physics Letters | Year: 2012

We demonstrate a novel method for active and passive Q-switching of a bulk laser source. The mechanism is based on the deflection of laser light through an electric channel of plasma that is temporarily created inside the resonator. The channel of plasma consists of an electric spark in air actuated with a spark gap. It acts as a spatio-temporal prism that momentarily enables the laser light to oscillate resonantly, thus triggering the creation of a laser pulse. Nanosecond pulses from a microchip laser source have been obtained with a limited timing jitter. © 2012 by Astro, Ltd.

Marie R.,University of Picardie Jules Verne | Labbani-Igbida O.,University of Picardie Jules Verne | Labbani-Igbida O.,XLim Institute | Mouaddib E.M.,University of Picardie Jules Verne
Proceedings - International Conference on Pattern Recognition | Year: 2012

The paper introduces a novel approach to place representation for robot localization and mapping. It uses classical invariance theory while proposing an adaptive kernel to omnidirectional images and exploiting only the main significant visual information in the images. The approach is validated in real world robot exploration and localization and compared to color histograms. © 2012 ICPR Org Committee.

Fahs H.,XLIM Institute | Hadjem A.,Orange S.A. | Lanteri S.,French Institute for Research in Computer Science and Automation | Wiart J.,Orange S.A.
IEEE Transactions on Antennas and Propagation | Year: 2011

The great majority of numerical calculations of the specific absorption rate (SAR) induced in human tissues exposed to microwaves are performed using the finite difference time-domain (FDTD) method and voxel-based geometrical models. The straightforward implementation of the method and its computational efficiency are among the main reasons for FDTD being currently the leading method for numerical assessment of human exposure to electromagnetic waves. However, the rather difficult departure from the commonly used Cartesian grid and cell size limitations regarding the discretization of very detailed structures of human tissues are often recognized as the main weaknesses of the method in this application context. In particular, interfaces between tissues where sharp gradients of the electromagnetic field may occur are hardly modeled rigorously in these studies. We present here an alternative numerical dosimetry methodology which is based on a high order discontinuous Galerkin time-domain (DGTD) method and adapted geometrical models constructed from unstructured triangulations of tissue interfaces, and discuss its application to the calculation of the SAR induced in head tissues. © 2011 IEEE.

Kobelke J.,Institute of Photonic Technology | Schuster K.,Institute of Photonic Technology | Litzkendorf D.,Institute of Photonic Technology | Schwuchow A.,Institute of Photonic Technology | And 7 more authors.
Optical Materials | Year: 2010

Modified core glass materials in silica-clad microstructured fibers (MOFs) promise efficient conversion of non-linear processes, e.g. for supercontinuum (SC) generation. We used extremely highly germanium-doped silica (max. 36 mol% GeO 2) and lanthanum aluminum silicate glasses with high lanthanum oxide concentration (max. 10 mol% La 2O 3) as core materials. The microstructured optical fibers (Ge-MOFs, La-MOFs) were prepared in five air ring architecture by a stack-and-draw technique using silica for the cladding region. The MOFs show loss minima of about 0.05 dB m 1 (Ge-MOF) and 1.3 dB m 1 (La-MOF) at a wavelength of 1.064 μm. Such Ge-MOFs and La-MOFs are compatible with conventional silica fibers giving low loss splices with standard single mode fibers. The non-linearity of the La-MOF is approximately two times higher than that of the Ge-MOF, but shows a significantly higher spectral loss. Ge-MOF and La-MOF can both produce similar ultra-broad band supercontinuum spectra from VIS (540 nm and 500 nm) to IR range (2400 nm and 2220 nm) by being pumped with a passively Q-switched Nd:YAG microchip laser. © 2010 Elsevier B.V. All rights reserved.

De Angelis A.,Xlim Institute | Couderc V.,Xlim Institute | Leproux P.,Xlim Institute | Labruyere A.,Xlim Institute | And 4 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

In the area of bioelectromagnetic studies there is a growing interest to understand the mechanisms leading to nanosecond electric fields induced electroporation. Real-time imaging techniques at molecular level could probably bring further advances on how electric fields interact with living cells. However the investigations are limited by the present-day lack of these kinds of advanced instrumentations. In this context, we present an innovative electro-optical pump-probe system. The aim of our project is to provide a performing and compact device for electrical stimulation and multiplex Coherent anti-Stokes Raman Scattering (M-CARS) imaging of biological cells at once. The system consists of a 1064 nm sub-nanosecond laser source providing both a monochromatic pump and a polychromatic Stokes optical beam used in a CARS process, as well as the trigger beam for the optoelectronic switchingbased electrical pulse generator. The polychromatic Stokes beam (from 600 to 1700 nm) results from a supercontinuum generation in a photonic crystal fiber (PCF). A detailed spectro-temporal characterization of such a broadband spectrum shows the impact of the nonlinear propagation in the fiber on the Stokes wave. Despite the temporal distortions observable on Stokes pulse profiles, their spectral synchronization with the pump pulse remains possible and efficient in the interesting region between 1100 nm and 1700 nm. The electrical stimulation device consists of a customized generator combining microstrip-line technology and lasertriggered photoconductive semiconductor switches. Our experimental characterization highlights the capability for such a generator to control the main pulse parameters (profile, amplitude and duration) and to be easily synchronized with the imaging system. We finally test and calibrate the system by means of a KDP crystal. The preliminary results suggest that this electro-optical system provides a suitable tool for real-time investigation of bioelectromagnetic interactions in the nanosecond and sub-nanosecond regime. © 2012 SPIE.

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