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  • Publication
    Métadonnées seulement
    Interferometric measurements beyond the coherence length of the laser source
    (2016-9-19) ; ; ;
    Salvadé, Yves
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    Przygodda, Frank
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    Rohner, Marcel
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    Meyer, Yves
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    Gloriot, Olivier
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    Llera, Miguel
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    Polster, Albert
    Interferometric measurements beyond the coherence length of the laser are investigated theoretically and experimentally in this paper. Thanks to a high-bandwidth detection, high-speed digitizers and a fast digital signal processing, we have demonstrated that the limit of the coherence length can be overcome. Theoretically, the maximal measurable displacement is infinite provided that the sampling rate is sufficiently short to prevent any phase unwrapping error. We could verify experimentally this concept using a miniature interferometer prototype, based on a frequency stabilized vertical cavity surface emitting laser. Displacement measurements at optical path differences up to 36 m could be realized with a relative stability better than 0.1 ppm, although the coherence length estimated from the linewidth and frequency noise measurements do not exceed 6.6 m.
  • Publication
    Métadonnées seulement
    Real-time Amyloid Aggregation Monitoring with a Photonic Crystal-based Approach
    (2013) ;
    Musi, Valeria
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    Descrovi, Emiliano
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    Paeder, Vincent
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    Hvozdara, Lubos
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    van der Wal, Peter
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    Lashuel, Hilal A.
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    Pastore, Annalisa
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    Herzig, Hans Peter
    We propose the application of a new label-free optical technique based on photonic nanostructures to real-time monitor the amyloid-beta 1-42 (A?(1-42)) fibrillization, including the early stages of the aggregation process, which are related to the onset of the Alzheimer's Disease (AD). The aggregation of A? peptides into amyloid fibrils has commonly been assocd. with neuronal death, which culminates in the clin. features of the incurable degenerative AD. Recent studies revealed that cell toxicity is detd. by the formation of sol. oligomeric forms of A? peptides in the early stages of aggregation. At this phase, classical amyloid detection techniques lack in sensitivity. Upon a chem. passivation of the sensing surface by means of polyethylene glycol, the proposed approach allows an accurate, real-time monitoring of the refractive index variation of the soln., wherein A?(1-42) peptides are aggregating. This measurement is directly related to the aggregation state of the peptide throughout oligomerization and subsequent fibrillization. Our findings open new perspectives in the understanding of the dynamics of amyloid formation, and validate this approach as a new and powerful method to screen aggregation at early stages. [on SciFinder(R)]
  • Publication
    Métadonnées seulement
    Si-Interdiffusion in heavily doped AIN-GaN-based quantum well intersubband photodetectors
    (2011) ; ;
    Martin, Denis
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    Grandjean, Nicolas
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    Kotsar, Yulia
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    Monroy, Eva
    We demonstrate the effect of rapid thermal annealing on heavily Si-doped AlN/GaN quantum wells. After 1000 °C annealing during 5, 10, and 20 min, the dominant effect was interdiffusion of Si rather than intermixing between the Al and Ga atoms. Both their original value and the magnitude of the changes after annealing reveal that intersubband absorption and photovoltage are related to two different optical transitions as follows: absorption occurs in the 1 to 2 intersubband transition, whereas photovoltage is due to a subsequent process from the 1 to 2 and the manifold of 2 to higher order transitions. © 2011 American Institute of Physics.
  • Publication
    Métadonnées seulement
    CO2 isotope sensor using a broadband infrared source, a spectrally narrow 4.4 μm quantum cascade detector and a Fourier spectrometer
    (2011) ; ;
    Hvozdara, L.
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    Herzig, H.-P.
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    Beck, M.
    Abstract: We report a prototype CO2 gas sensor based on a simple blackbody infrared source and a spectrally narrow quantum cascade detector (QCD). The detector absorption spectrum is centered at 2260 cm(-1) (4.4 um) and has a full width at half maximum of 200 cm(-1)(25 meV). It covers strong absorption bands of two spectrally overlapping CO2 isotopomers, namely the P-branch of 12CO2 and the R-branch of 13CO2. Acquisition of the spectral information and data treatment were performed in a Fourier transform infrared (FTIR) spectrometer. By flushing its sample compartment either with nitrogen, dry fresh air, ambient air, or human breath, we were able to determine CO2 concentrations corresponding to the different gas mixtures. A detection limit of 500 ppb was obtained in these experiments.
  • Publication
    Métadonnées seulement
    Performance Improvement of AIN-GaN-Based Intersubband Detectors by Using Qantum Dots
    (2010) ; ;
    Kandaswamy, Prem K.
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    Das, Aparna
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    Valdueza-Felip, Sirona
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    Monroy, Eva