Pulsed Frequency Shifted Feedback Laser for Accurate Long Distance Measurements: Beat Order Determination

Long-distance measurements (10 m - 1000 m) with an accuracy of 10-7 is a challenge for many applications. We show that it is achievable with Frequency Shifted Feedback (FSF) laser interferometry technique, provided that the determination of the radio frequency beat order be made without ambiguity and on a time scale compatible with atmospheric applications. Using the pulsed-FSF laser that we developed for laser guide star application, we propose and test, up to 240 m, a simple method for measuring the beat order in real time. The moving-comb and Yatsenko models are also discussed. The first of these models fails to interpret our long-distance interferometry results. We show that the accuracy of long-distance measurements depends primarily on the stabilization of the acoustic frequency of the modulator

Intracavity absorption spectroscopy with a turbulent detuned actively mode-locked Ti:sapphire laser

International audienceIntracavity laser absorption spectroscopy (ICLAS) is an extremely sensitive method for the detection of very weak absorptions. However, the conventional use of multimode lasers has thus far significantly reduced its ability to detect in situ molecules and its sensitivity. We propose the use of a new type of laser that overcomes these limitations: the turbulent detuned actively mode-locked (TDAM) Ti:sapphire laser, which owing to its short coherence length, eliminates harmful intracavity interferences. The proposed technique called TDAM-ICLAS is furthermore highly sensitive to intracavity absorption, continuously tunable and has no frequency chirp

Use of single-walled carbon nanotubes for near-infrared fluorescence within inner tissues in C. elegans

Anglès: Imaging and tracking long distance transport of proteins such as molecular motors with conventional fluorescence methodologies is nearly impossible mainly due to photobleaching. In this work we demonstrate that DNA-SWNTs are very convenient tagging particles for in vivo tracking of proteins due to their low toxicity and bright and stable fluorescence. Also, soft lithography is used to build a microfluidic trap for in vivo fluorescence imaging in C.elegans.Castellà: Hacer imágenes y seguir el transporte de proteínas como los motores moleculares a lo largo de distancias largas con técnica de fluorescencia convencionales es practicanete imposible debido al "photobleaching". En esta tesis demostramos que los ADN-SWNTs son unos marcadores de proteínas in vivo muy buenos gracias a su baja toxicidad y su fluorescencia estable e intensa. Además se utiliza litografía blanda para construir una trampa microfluidica para immobilizar un C.elegans y obtener imágenes de fluorescencia in vivo.Català: Fer imatges i seguir el transport de proteïnes com ara motors moleculars en distàncies llargues amb mètodes de fluorescència convencionals és quasi impossible a causa del "photobleaching". En aquesta tesi demostrem que els ADN-SWNTs són uns marcadors de proteïnes in vivo molt bons gracies a la seva baixa toxicitat i la seva fluorescència estable i intensa. A més, s'utilitza litografía tova per construir una trampa microfluidica per immobilitzar un C.elegans. i obtenir-ne imatges de fluorescència in vivo

Distritos de innovación en el mundo

El 20è aniversari del districte d’innovació de Barcelona, el 22@Barcelona, justifica plenament aquest número especial. Actors clau del món acadèmic, organitzacions i institucions de diversos districtes d'innovació d'arreu del món s'han sumat a aquest projecte de celebració que s'ha materialitzat en la col·lecció d'articles que conformen “Districts of Innovation in the World”. El resultat és una recopilació única d'experiències, anàlisis i avaluacions que evidencien la rellevància dels districtes d'innovació com a eines per al desenvolupament urbà, econòmic i social, però també com a nuclis urbans de producció de tecnologia i innovació. Beneficiat d'anys d'intercanvi d'idees i col·laboració mútua, aquest número especial ofereix, des d'una perspectiva evolutiva, una anàlisi de les transicions, adaptacions i mutacions que han experimentat els districtes d'innovació arreu del món.The 20th anniversary of the innovation district of Barcelona, the 22@Barcelona, provides the rationale for this special issue. Key actors in the academia, organisations and institutions from several innovation districts around the world, have joined this celebration project that has materialized in the collection of articles that conform “Districts of Innovation in the World”. The result is a unique compilation of experiences, analysis and evaluations that evidence the relevance of innovation districts as tools for urban, economic and social development but also as urban cores of production of technology and innovation. Benefiting from years of exchange of ideas and mutual collaboration, this special issue offers, from an evolutionary perspective, an analysis of the transitions, adaptations and mutations that innovation districts have experienced around the world.El 20 aniversario del distrito de innovación de Barcelona, el 22@Barcelona es la principal motivación de este número especial. Figuras clave del mundo académico, organizaciones e Instituciones de diversos distritos de innovación de todo el mundo se han reunido para este projecto de celebración que ha acabado materializándose en el conjunto de artículos que conforman este “Districts of Innovation in the World”. El resultado es una compilación única de experiències, anàlisis y evaluaciones que ponen en evidencia la relevancia de los distritos de innovación como herramientas para el desarrollo urbano, económico y social, así como para configurar centros urbanos de producción de tecnologia e innovación. Apoyándose en años de intercambio de idees y de colaboración mutua entre los autores de este número especial, ofrecemos desde una perspectiva evolutiva un anàlisis de las transiciones, adaptaciones y mutacions que los distritos de innovación han experimentado en el mundo

Statistical properties of frequency shifted feedback lasers

International audienceWe evidence experimentally the statistical properties of frequency shifted feedback (FSF) lasers through measurements of the homodyne beat signal and interferometric autocorrelation of a dye FSF laser at the output of a Michelson interferometer. The FSF laser is found to show thermal fluctuations and photon bunching. Moreover whereas the degree of first-order coherence vanishes beyond the coherence length of the FSF source, the degree of second-order coherence exhibits periodic revivals far beyond the coherence length, with a period equal to the cavity roundtrip time. Our observations are in good agreement with the theoretical treatment of Yatsenko et al. [L.P. Yatsenko, B.W. Shore, K. Bergmann, Opt. Comm. 236 (2004) 183] and validate the description of the output field of a FSF laser by a broadband cyclostationary thermal field

λ/2 fringe-spacing interferometer

International audienceThe precision of interferometry is directly linked to the fringe spacing of the recorded interferogram. Whereas all interferometric devices show a fringe spacing equal to a wavelength of the laser light we present a novel scheme of a two-beam interferometer exhibiting a fringe spacing reduced by a factor of 2; the direct detection of the beat signal is replaced with the monitoring of the fluorescence of a twofold degenerate atomic system resonant with the laser. The λ/2 fringe spacing in the fluorescence signal is demonstrated with a hot sodium vapor excited by a broadband laser tuned to the D1 line. In the saturation regime, the dark fringes are expected to be extremely narrow, leading to the possibility of nanoscale displacement measurements or atom localization

Coherence properties of modeless lasers

International audienceMost of classical light sources show a close similarity between their first and second order correlation functions (resp. g(1) and g(2)) functions. We present here the original coherence properties of a peculiar type of laser named modeless laser or Frequency Shifted Feedback (FSF) laser where the g(1) and g(2) functions show a different behaviour. We calculate and evidence experimentally the first and second order correlation functions of modeless lasers, through measurements of the homodyne beat signal and interferometric autocorrelation of a dye FSF laser at the output of a Michelson interferometer. Whereas the degree of first-order coherence vanishes beyond the coherence length of the FSF source, the degree of second-order coherence exhibits periodic revivals far beyond the coherence length, with a period equal to the cavity roundtrip time. Our observations are in good agreement with the theoretical treatment of Yatsenko et al. (Opt. Comm. 282 (2009) 300) [1]