Academic literature on the topic 'Conversions Stokes et anti-Stokes'
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Journal articles on the topic "Conversions Stokes et anti-Stokes"
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TAILLEUX, RÉMI. "On the energetics of stratified turbulent mixing, irreversible thermodynamics, Boussinesq models and the ocean heat engine controversy." Journal of Fluid Mechanics 638 (October 20, 2009): 339–82. http://dx.doi.org/10.1017/s002211200999111x.
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In this paper, the available potential energy (APE) framework of Winters et al. (J. Fluid Mech., vol. 289, 1995, p. 115) is extended to the fully compressible Navier–Stokes equations, with the aims of clarifying (i) the nature of the energy conversions taking place in turbulent thermally stratified fluids; and (ii) the role of surface buoyancy fluxes in the Munk & Wunsch (Deep-Sea Res., vol. 45, 1998, p. 1977) constraint on the mechanical energy sources of stirring required to maintain diapycnal mixing in the oceans. The new framework reveals that the observed turbulent rate of increase in the background gravitational potential energy GPEr, commonly thought to occur at the expense of the diffusively dissipated APE, actually occurs at the expense of internal energy, as in the laminar case. The APE dissipated by molecular diffusion, on the other hand, is found to be converted into internal energy (IE), similar to the viscously dissipated kinetic energy KE. Turbulent stirring, therefore, does not introduce a new APE/GPEr mechanical-to-mechanical energy conversion, but simply enhances the existing IE/GPEr conversion rate, in addition to enhancing the viscous dissipation and the entropy production rates. This, in turn, implies that molecular diffusion contributes to the dissipation of the available mechanical energy ME = APE + KE, along with viscous dissipation. This result has important implications for the interpretation of the concepts of mixing efficiency γmixing and flux Richardson number Rf, for which new physically based definitions are proposed and contrasted with previous definitions.The new framework allows for a more rigorous and general re-derivation from the first principles of Munk & Wunsch (1998, hereafter MW98)'s constraint, also valid for a non-Boussinesq ocean: where G(KE) is the work rate done by the mechanical forcing, Wr, forcing is the rate of loss of GPEr due to high-latitude cooling and ξ is a nonlinearity parameter such that ξ = 1 for a linear equation of state (as considered by MW98), but ξ < 1 otherwise. The most important result is that G(APE), the work rate done by the surface buoyancy fluxes, must be numerically as large as Wr, forcing and, therefore, as important as the mechanical forcing in stirring and driving the oceans. As a consequence, the overall mixing efficiency of the oceans is likely to be larger than the value γmixing = 0.2 presently used, thereby possibly eliminating the apparent shortfall in mechanical stirring energy that results from using γmixing = 0.2 in the above formula.
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Jones, Callum M. S., Adilet Zhakeyev, and Jose Marques-Hueso. "(Invited) Calibration of Upconverting Materials and Nanoprobes." ECS Meeting Abstracts MA2023-02, no. 63 (2023): 2990. http://dx.doi.org/10.1149/ma2023-02632990mtgabs.
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Upconversion has attracted much attention for the potential applications of nanomaterials and bulk materials. Upconversion nanoprobes and sensors rely on the non-linear emission of the reporters, which present a low efficiency due to their anti-Stokes nature. For these two reasons, the materials require accurate and contrastable efficiency measurements, typically by measuring the absolute upconversion quantum yield (UCQY). The methodology for such measurements will vary from traditional photoluminescence quantum yield techniques that have been applied for downshifting materials [1]. Effects like the scattering, broadband absorption and reemission, inner-filter effects, thickness, self-absorption, and temperature, have to be considered [2]. This presentation will focus on some of these effects. The scattering has usually been neglected, however systems with scattering can increase the power density and subsequently the UCQY, as demonstrated both experimentally and via simulations [3]. Furthermore, this energy concentration also provides a new method for identifying the refractive index of phosphors, which is useful since some phosphors cannot be produced in macroscopic sizes. Broadband characterisation enables a route for characterisation exploiting the wide energy levels at the near-infrared. However, it introduces new challenges such as reemission [4]. In the case of applications that use a thick upconverted, the thickness is also a key parameter that can be responsible up to 50% of the emission [5]. Finally, one of the applications that is been intensively researched is the use of upconverting and downshifting nanoparticles as temperature reporters. Absolute upconversion photoluminescence quantum yield characterisation for different probes will be presented with a modified integrating sphere that allows in-situ absorption and emission measurements. References: [1] Callum M. S. Jones, Anna Gakamsky & Jose Marques-Hueso (2021) The upconversion quantum yield (UCQY): a review to standardize the measurement methodology, improve comparability, and define efficiency standards, Science and Technology of Advanced Materials, 22:1, 810-848, DOI: 10.1080/14686996.2021.1967698 [2] Callum M. S. Jones, Daniel Biner, Stavros Misopoulos, et al. Optimized photoluminescence quantum yield in upconversion composites considering the scattering, inner-filter effects, thickness, self-absorption, and temperature. Sci Rep 11, 13910 (2021). DOI:10.1038/s41598-021-93400-8 [3] Callum M. S. Jones, Nikita Panov, Artiom Skripka, et al., "Effect of light scattering on upconversion photoluminescence quantum yield in microscale-to-nanoscale materials," Opt. Express 28, 22803-22818 (2020). DOI: 10.1364/OE.398353 [4] Sean K. W. MacDougall, Aruna Ivaturi, Jose Marques-Hueso, et al; “Measurement procedure for absolute broadband infrared up-conversion photoluminescent quantum yields: Correcting for absorption/re-emission”. Rev Sci Instrum, 85 (6), 063109 (2014). DOI:10.1063/1.4881537 [5] Alessandro Boccolini, Jose Marques-Hueso, and Bryce S. Richards, "Self-absorption in upconverter luminescent layers: impact on quantum yield measurements and on designing optimized photovoltaic devices," Opt. Lett. 39, 2904-2907 (2014). DOI: 10.1364/OL.39.002904 Figure 1
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Ivanov, Nikolay, Marina Zasimova, Evgueni Smirnov, and Detelin Markov. "Evaluation of mean velocity and mean speed for test ventilated room from RANS and LES CFD modeling." E3S Web of Conferences 85 (2019): 02004. http://dx.doi.org/10.1051/e3sconf/20198502004.
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The paper presents and discusses data for the ventilation airflow in an isothermal room corresponding to the Nielsen et al. (1978) test computed with Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) approaches. As LES computations provide directly both the speed and velocity components data, the difference between the mean speed and mean velocity values is computed and discussed. For the RANS computations that give the mean velocity data only, application of the velocity-to-speed conversion procedure based on the turbulence kinetic energy field provided by a turbulence model resulted in accurate mean speed evaluation.
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Scherman, Michael, Joanna Barros, Rosa Santagata, Alexandre Bresson, and Brigitte Attal-Tretout. "Thermométrie Raman cohérente pour l'étude de la combustion." Photoniques, no. 96 (May 2019): 23–29. http://dx.doi.org/10.1051/photon/20199623.
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La combustion est un sujet d’intérêt pour une large variété de domaines d’applications civils ou militaires. Comprendre les phénomènes physico-chimiques à l’oeuvre dans ces milieux complexes, et les décrire à l’aide de modèles éprouvés, sont des enjeux majeurs qui requièrent des mesures fiables et quantitatives. La spectroscopie par diffusion Raman anti-Stokes cohérente (DRASC ou CARS en anglais) a démontré des performances inégalées pour la mesure de température. Cette technique a été implémentée avec de nombreuses architectures laser, et appliquée avec succès à un large éventail de milieux.
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Huang, Huining, Haifeng Zhou, Juan Zhou, et al. "Correction: Enhanced anti-Stokes luminescence in LaNbO4:Ln3+ (Ln3+ = Yb3+, Er3+/Ho3+/Tm3+) with abundant color." RSC Advances 7, no. 31 (2017): 19305. http://dx.doi.org/10.1039/c7ra90049j.
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Correction for ‘Enhanced anti-stocks luminescence in LaNbO<sub>4</sub>:Ln<sup>3+</sup> (Ln<sup>3+</sup> = Yb<sup>3+</sup>, Er<sup>3+</sup>/Ho<sup>3+</sup>/Tm<sup>3+</sup>) with abundant color’ by Huining Huang et al., RSC Adv., 2017, 7, 16777–16786.
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Deckert, Volker, Tanja Deckert-Gaudig, Dana Cialla-May, et al. "Laser spectroscopic technique for direct identification of a single virus I: FASTER CARS." Proceedings of the National Academy of Sciences 117, no. 45 (2020): 27820–24. http://dx.doi.org/10.1073/pnas.2013169117.
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From the famous 1918 H1N1 influenza to the present COVID-19 pandemic, the need for improved viral detection techniques is all too apparent. The aim of the present paper is to show that identification of individual virus particles in clinical sample materials quickly and reliably is near at hand. First of all, our team has developed techniques for identification of virions based on a modular atomic force microscopy (AFM). Furthermore, femtosecond adaptive spectroscopic techniques with enhanced resolution via coherent anti-Stokes Raman scattering (FASTER CARS) using tip-enhanced techniques markedly improves the sensitivity [M. O. Scully,et al.,Proc. Natl. Acad. Sci. U.S.A.99, 10994–11001 (2002)].
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Wakolo, Solomon Wekesa, Hiromichi Nishiyama, Kenji Miyatake, and Junji Inukai. "Chemical States of Water in Anion Exchange Membrane for Fuel Cells Using Raman and Coherent Anti-Stokes Raman Spectroscopies." ECS Meeting Abstracts MA2023-02, no. 65 (2023): 3163. http://dx.doi.org/10.1149/ma2023-02653163mtgabs.
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Purpose Low membrane durability remains a major challenge in anion exchange membrane fuel cells (AEMFCs). This is despite the AEMFCs’ proven potential to eliminate the dependency of Fuel cells on Pt catalysts and bring about the mass commercialization of the technology. This problem can be effectively addressed through combined optimization of the AEMFCs’ operating conditions during evaluation, followed by finetuning of the membrane chemistry to address any observed weaknesses. After synthesis, water distribution is the primary operation condition determining a given AEM’s performance and lifespan [1]. This is partly because water affects the ionic conductivity and, thus, maximum current density, which is known to play a significant role in the longevity of membranes. Therefore, establishing the water distribution during power generation for any given membrane is highly desirable. For this to happen, suitable and reliable techniques must exist to measure and compare the water distribution in situ and operando. In this paper, we used in-house assembled Raman spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS) systems to measure the water in an operational AEMFC for the first time. CARS comes with a high time resolution of 0.1 s, which is essential in the transient response study of FCs. Experimental Method QPAF-4 membrane film (Fig. 1) of the thickness of 30 µm and IEC of 2.0 meq g-1 was solution cast as reported [2]. The cell was then assembled, as reported [3]. An airtight transparent quartz window 200 μm thick was mounted at the cathode endplate for optical access to the QPAF-4 membrane through a 500 mm pinhole in the GDE. A thin Pt disk was placed on the opposite side of the membrane to reflect the signal to the spectrometer through the ×50 objective lens used. For Raman spectroscopy, a 632 nm, 1 mW laser with 5.5 min total exposure was used. For CARS, an 11 mW 785nm pump laser and 16 mW Stokes laser with 200 ms total exposure were used. The flow rate was 100 ml min-1 for all gases. The cell temperature was maintained at 60 °C. The relative humidity of the gas varied from 30% to 100% in steps of 10% RH. The system was allowed to stabilize for 3 hours at each humidity level before measurement. Results and discussion Figures 2 and 3 show the normalized in situ spectra recorded at the center of the membrane at different relative humidity values using CARS and Raman, respectively. The peak positions are comparable. However, the OH peak in CARS is taller relative to C=C than in Raman. CARS signal intensity is generally stronger than Raman [3]. Within the CARS peak, the purely OH portion of the signal is more prominent relative to the rest of the peak than in Raman. This is attributed to the fact that the Infrared laser associated with the stokes light (817-1144nm) of CARS is known to be more sensitive to OH vibration than the lower wavelength laser (632nm) used in Raman [4]. Conclusion We successfully developed a 785nm CARS system capable of operando water measurement in AEMFCs. The results from this technique are comparable to those from micro-Raman spectroscopy but with better signal intensity and time resolution. This increases the number of practical methods available to researchers interested in measuring water content in AEMFCs allowing for faster development of the technology. The water distribution results during power generation will be discussed at the conference. With CARS, higher temporal/time resolution is achieved, which is advantageous when cell response needs to be studied. References [1] K. Otsuji et al. J. Power Sources, 522, 230997 (2022). [2] H. Ono et al. J. Mater. Chem. A, 5, 24804 (2017). [3] H. Nishiyama et al. J. Phys. Chem. C, 124, 9703 (2020). [4] Y. Horiba Jobin, “Raman Spectroscopy for Analysis and Monitoring,” (2017). Figure 1
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Chaussard, F., N. Le Cong, B. Lavorel, et al. "Spectroscopie Raman Anti-Stokes Cohérente femtoseconde (DRASC – fs) : expériences et modélisation dans le cas du mélange H2 – N2 à basse pression." Journal de Physique IV (Proceedings) 135, no. 1 (2006): 155–56. http://dx.doi.org/10.1051/jp4:2006135038.
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Kaminskii, A. A., L. Bohat�, P. Becker, et al. "Non-centrosymmetric Y(HCOO)3 � 2 H2O crystal. A new inorganic material for Raman lasers with large frequency shift of three promoting vibration modes of its [O-CH-O]- formate anions: effective high-order Stokes and anti-Stokes generation and cascaded self-frequency [?(3)(SRS) ??(2)(SHG, SFM)] and [?(2)(SHG, SFM) ??(3)(SRS)] conversions." physica status solidi (a) 201, no. 14 (2004): 3200–3216. http://dx.doi.org/10.1002/pssa.200406893.
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Lin, Jeffrey, Carlo Scalo, and Lambertus Hesselink. "High-fidelity simulation of a standing-wave thermoacoustic–piezoelectric engine." Journal of Fluid Mechanics 808 (October 26, 2016): 19–60. http://dx.doi.org/10.1017/jfm.2016.609.
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We have carried out wall-resolved unstructured fully compressible Navier–Stokes simulations of a complete standing-wave thermoacoustic–piezoelectric engine model inspired by the experimental work of Smoker et al. (J. Appl. Phys., vol. 111 (10), 2012, 104901). The model is axisymmetric and comprises a 51 cm long resonator divided into two sections: a small-diameter section enclosing a thermoacoustic stack and a larger-diameter section capped by a piezoelectric diaphragm tuned to the thermoacoustically amplified mode (388 Hz). The diaphragm is modelled with multi-oscillator broadband time-domain impedance boundary conditions (TDIBCs), providing higher fidelity over single-oscillator approximations. Simulations are first carried out to the limit cycle without energy extraction. The observed growth rates are shown to be grid convergent and are verified against a numerical dynamical model based on Rott’s theory. The latter is based on a staggered grid approach and allows jump conditions in the derivatives of pressure and velocity in sections of abrupt area change and the inclusion of linearized minor losses. The stack geometry maximizing the growth rate is also found. At the limit cycle, thermoacoustic heat leakage and frequency shifts are observed, consistent with experiments. Upon activation of the piezoelectric diaphragm, steady acoustic energy extraction and a reduced pressure amplitude limit cycle are obtained. A heuristic closure of the limit cycle acoustic energy budget is presented, supported by the linear dynamical model and the nonlinear simulations. The developed high-fidelity simulation framework provides accurate predictions of thermal-to-acoustic and acoustic-to-mechanical energy conversion (via TDIBCs), enabling a new paradigm for the design and optimization of advanced thermoacoustic engines.
Dissertations / Theses on the topic "Conversions Stokes et anti-Stokes"
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Cheroura, Youcef. "Photoconversion et exaltation plasmonique de nanoparticules de β-NaGdF4 pour potentielles applications photovoltaïques sur silicium". Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2021. http://www.theses.fr/2021UCFAC023.
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Un système multifonctionnel a été élaboré pour être utilisé comme double capteur de lumière ultraviolette (UV) et proche infrarouge (NIR) et permettant de convertir ces rayonnements par des mécanismes Stokes (DS-DC) et anti-Stokes (UC) en lumière visible susceptible d’accroître le rendement des cellules photovoltaïques. Des nano-bâtonnets ( 140 nm x 60 nm) de β-NaGdF4 monodopés par Eu3+, Pr3+, Er3+ et codopés par Yb3+ ont été synthétisés de façon reproductible par co-précipitation (conditions optimisées : 150°C, 60 min). Les propriétés structurales et morphologiques ont été caractérisées par diffraction des rayons X, spectroscopie infrarouge, Raman et microscopie électronique (MET) confirmant la qualité des matériaux synthétisés. L’utilisation des propriétés de sonde structurale de l’ion Eu3+ a permis d’identifier et de discuter de l’ordre local en s’appuyant sur la théorie de Judd-Ofelt. L’analyse des propriétés de fluorescence a été menée sous excitations impulsionnelle et continue. Les canaux de désexcitation radiative et de transfert d’énergie pour les deux processus DC et UC, pour chaque système, ont été identifiés et discutés en s’appuyant sur l’évolution des intensités de fluorescence en fonction de la puissance de pompe en régime continu et sur les cinétiques de décroissances temporelles sous excitations UV et NIR. Une attention particulière a été accordée au système Er3+/Yb3+ pour lequel un couplage par effet plasmonique a été envisagé avec des nanoparticules métalliques (NPMs) de métaux nobles or et argent. Selon la nature, la forme et la taille des NPMs, des exaltations ou des atténuations des intensités de fluorescence, s’accompagnant dans certains cas d’un accroissement des taux de décroissance temporelle ont été observées. Elles sont discutées en considérant deux processus principaux, la diffusion et l’effet Purcell<br>A multifunctional system was developed to be used as a dual ultraviolet (UV) and near infrared (NIR) light harvester and photo-converters by Down (DS-DC) and Up Conversions (UC) in visible light to enhance the light trapping properties of thin-film solar cells. Nanorods ( 140 nm x 60 nm) of β-NaGdF4 singly doped by Eu3+, Pr3+, Er3+ and co-doped by Yb3+ were synthesized by co-precipitation method (optimized conditions: 150°C, 60 min). The structural and morphological properties were characterized by X-ray diffraction, infrared spectroscopy, Raman and electron microscopy (TEM) confirming the quality of the elaborated materials. Using the structural probe properties of the Eu3+ ion, local order was identified and discussed on the basis of Judd-Ofelt theory. The analysis of the fluorescence properties was carried out under pulsed and cw excitations. The radiative de-excitation and energy transfer channels for both DC and UC processes, occurring in each system, have been identified and discussed based on the evolution of fluorescence intensities as a function of continuous pump power and on the kinetics of luminescence decays under UV and NIR excitations. Particular attention was paid to the Er3+/Yb3+ system for which a coupling by plasmonic effect was considered with metallic nanoparticles (NPMs) of noble metals gold and silver. Depending on the nature, shape and size of the NPMs, enhancements or attenuations of fluorescence intensities, in addition in some cases to an increase in decaying rates have been observed. They are discussed considering two main processes, scattering and the Purcell effects
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ZHANG, XIAO. "Excitation de la fluorescence anti-stokes de l'ion holmium trivalent dans les fluorites et le fluorure de lanthane." Reims, 1996. http://www.theses.fr/1996REIMS008.
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Ce travail presente une etude de la conversion rouge-vert et rouge-bleu par l'ion holmium trivalent dans les fluorites et le fluorure de lanthane. Une telle conversion peut s'effectuer par differents mecanismes: le processus d'absorptions successives, le transfert d'energie et l'avalanche de photons. Une connaissance approfondie de ces mecanismes est necessaire car ils sont utilises depuis une dizaine d'annees, pour realiser des lasers emettant dans le vert et bleu lorsqu'on les excite dans le rouge ou le proche infrarouge. Dans les cristaux de structure fluorite, l'ion holmium trivalent se substitue au cation divalent et peut occuper differents sites cristallographiques a cause de la necessite d'une compensation de charge. Avec la technique de spectroscopie par selection de sites effectuee avec un laser a colorant accordable dans le rouge, ces differents sites peuvent etre etudies separement. Au contraire, dans le fluorure de lanthane, l'ion holmium n'occupe qu'un seul site. Dans tous les cas, les etudes spectroscopique et dynamique des fluorescences stokes et anti-stokes revelent que les principaux mecanismes d'excitation de l'ion holmium sont des absorptions successives a deux photons et des transferts d'energie. Le processus d'absorptions successives via un niveau dont la duree de vie est suffisamment longue pour favoriser l'absorption du second photon a ete identifie avec les sites isoles. Le processus de transfert d'energie a ete observe essentiellement pour les paires mais aussi entre des ions holmium plus eloignes. L'etude dynamique revele differents processus de transferts, impliquant deux ions holmium excites soit sur le meme niveau d'energie soit sur deux niveaux differents. Avec le fluorure de cadmium codope holmium et ytterbium, l'ion ytterbium joue le role de pont pour transferer l'energie d'excitation d'un ion holmium a l'autre et de barriere pour empecher les relaxations croisees entre les ions holmium
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Goldner, Philippe. "Processus de paires dans une perovskite hexagonale : luminescence anti-stokes dans les systemes erbium-erbium et erbium-ytterbium." Paris 6, 1993. http://www.theses.fr/1993PA066376.
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L'etude spectroscopique de differents processus de conversion de frequence est presentee dans cscdbr#3. Dope ou codope par l'erbium et l'ytterbium. Les impuretes trivalentes forment dans cette matrice des paires compensees en charge de facon quasi-exclusive. Une etude par spectroscopie a haute resolution et a basse temperature, de structures de paires a mis en evidence, outre les dimeres symetriques (lacune centrale), un complexe asymetrique (lacune laterale). Dans ce cas, les ions sont couples par un fort transfert d'energie. Dans les echantillons codopes, des paires mixtes ont ete identifiees. D'autre part, un fort couplage entre ions d'une meme paire a ete observe lors de l'etude de la conversion visible-ultraviolette. La position en energie et la duree de vie de niveaux de l'erbium situes a haute energie ont ete mesurees par absorption dans l'etat excite. A partir de ces resultats, l'ensemble des processus donnant naissance aux emissions anti-stokes ont ete analyses a travers la dynamique de fluorescence, ce qui a revele l'importance des mecanismes de competition entre relaxations croisees. Enfin la formation de paires mixtes s'est revelee defavorable au rendement de conversion infrarouge-visible
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Gachet, David. "Microscopie CARS (Coherent anti-Stokes Raman scattering). Génération du signal au voisinage d'interfaces et à l'intérieur d'une cavité Fabry-Perot." Aix-Marseille 3, 2007. http://www.theses.fr/2007AIX30060.
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Le processus de diffusion "CARS" (Cohérent anti-Stokes Raman scattering) est une technique de spectroscopie qui donne accès à une information sur les modes vibrationnels intra-moléculaires de l'échantillon étudié. L'introduction de ce processus de diffusion en microscopie a été pour la première fois proposée en 1982. Elle a été par la suite mise en oeuvre dans une configuration colinéaire en 1999. La génération du signal en microscopie CARS a dès lors été étudiée sur des exemples simples. Dans ce mémoire de thèse, nous étendons l'analyse du signal en microscopie CARS en utilisant un formalisme purement vectoriel. En particulier, nous introduisons dans cette étude le coefficient de dépolarisation Raman du mode vibrationnel étudié et analysons son influence sur les diagrammes de rayonnement en champ lointain du signal CARS. Dans une seconde partie, nous nous intéressons à la génération du signal CARS au voisinage d'interfaces transverses et axiales. D'une part, nous présentons une méthode très simple pour obtenir des spectres CARS affranchis de tout fond non-résonant (c'est-à-dire similaires à des spectres Raman purs) au voisinage d'interfaces transverses, en utilisant une excitation conventionnelle. D'autre part, nous présentons une étude expérimentale et théorique de la modification du contraste d'une interface axiale en fonction du désaccord spectral des lasers d'excitation autour d'une résonance vibrationnelle. Ces effets sont intrinsèquement liés à la nature à la fois cohérente et résonante du processus de diffusion CARS. Enfin, dans le but de d'augmenter la sensibilité de la microscopie CARS, nous proposons de générer le signal CARS au voisinage d'une structure résonante. A cet effet, nous menons des étude théorique et expérimentale de la génération du signal CARS dans une cavité Fabry-Perot. Nous démontrons des effets intéressants pour des applications en microscopie CARS, qui incluent une exaltation du signal, une augmentation de sa directivité ainsi qu'une symétrisation des signaux générés en avant et en arrière de l'objet émetteur. Cette dernière étude illustre l'influence de l'environnement électromagnétique sur la génération de lumière<br>Coherent anti-Stokes Raman scattering ("CARS") is a spectroscopic technique that gives access to intra-molecular vibrational information. It was first proposed as a contrast mechanism in microscopy in 1982, and was implemented under a convenient colinear configuration in 1999. Since then, the signal generation in CARS microscopy has been studied in the litterature on some simple configurations. In this PhD dissertation, we extend the CARS signal generation study in isotropic media using a full-vectorial formalism. In particular, we introduce CARS signal dependency on the Raman depolarisation ratio and study theoretically its influence on far-field radiation patterns. In another part, we investigate the CARS signal generation in the vicinity of transverse and axial interfaces. On the one hand, a very simple method to obtain background free CARS spectra (i. E. Similar to pure Raman spectra) near transverse interfaces, with conventional excitation, is presented. One the other hand, we show theoretically and experimentally how the excitation detuning modifies the contrast of axial interfaces. These effects are tightly bound to the coherent and resonant nature of CARS. Finally, in order to enhance CARS microscopy sensitivity, we propose to generate the CARS signal near a resonant structure. In this purpose, we lead theoretical and experimental studies of CARS signal generation in a Fabry-Perot cavity. We show how this cavity enhances signal, increases its directivity and symetrise Fwd-CARS and Epi-CARS signals. Such effects are interesting for CARS microscopy. This last study illustrates the electromagnetic environment influence on light emission
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Boulma, El-Haine. "Etude des propriétés spectroscopiques des ions erbium et thulium trivalents dilués dans des cristaux de KY3F10." Reims, 2007. http://www.theses.fr/2007REIMS025.
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La conversion de lumière vers les hautes fréquences s'effectue selon trois types de mécanismes d'excitation: absorptions successives de plusieurs photons, transfert d'énergie entre les ions dans un état excité et l'avalanche de photons. Ce dernier processus est un effet collectif basé sur un transfert d'énergie à partir d'un ion à l'état excité vers un ion à l'état fondamental. Sous certaines conditions, ces transferts peuvent conduire à une réaction en chaîne entraînant une importante augmentation de l'intensité de la fluorescence anti-Stokes. L'objet de ce travail est l'étude systématique de la fluorescence anti-Stokes des ions de terres rares trivalents dans les cristaux du type fluorite. Les études que nous présentons ont été effectuées en utilisant une excitation monochromatique autour de 650 nm fournie par un laser à colorant. Nous avons étudié plus particulièrement les ions erbium et thulium dilués dans les monocristaux de KY3F10. Cette étude nous a permis de déterminer les sous niveaux Stark des différents multiplets 2S+1LJ des ions Er3+ et Tm3+ à la température de l'azote liquide avec une très bonne précision. Nous avons aussi exposé les résultats relatifs à la dynamique de la fluorescence anti-Stokes en analysant la variation de l'intensité de la fluorescence en fonction de la puissance d'excitation et en effectuant des mesures de durées de vie. Nous rapportons aussi les résultats d'une étude spectroscopique et dynamique des émissions anti-Stokes du même cristal de KY3F10 dopé par des ions Tm3+ démontrant l'effet de sensibilisation des ions Er3+, présents à l'état de traces, sur les raies d'absorption dans l'état excité du Tm3+<br>The conversion of light towards high frequencies is carried out according to three excitation mechanism types: successive absorptions of several photons, the excited-state energy transfer between ions and the photons avalanche. This last process is a collective effect based on an energy transfer between an excited ion and an unexcited ion. Under certain conditions, these transfers can lead to a chain reaction inducing an important increase of anti-Stokes fluorescent intensity. The object of this work is the systematic study of the anti-Stokes fluorescence of the trivalent rare earth ions in the fluorite crystals. The studies, which we present, are recorded by using a monochromatic excitation around 650 nm provided by a tunable dye laser. I have studied more particularly the erbium and thulium diluted ions in the KY3F10 single crystals. This study permits to determine Starks sub-levels of the various 2S+LJ multiplets of Er3+ and Tm3+ ions at liquid nitrogen temperature with a very good precision. We expose also the results relating to the dynamics of anti-Stokes fluorescence, by analyzing the variation of the fluorescence intensity as a function of the excitation power and by taking measurements of lifetimes. We also report the results of a spectroscopic study of anti-Stokes emissions from a Tm3+-doped KY3F10 crystal demonstrating the sensitized effect of Er3+ ions, present as trace impurities, on the excited-state absorption lines of Tm3. In addition to Er3+ ion, the Ho3+ ion does not increase the possibilities of resonant transfer with the Tm3+ ion
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Joly, Véronique. "Etude théorique et expérimentale des mécanismes cinétiques dans le laser iode-oxygène chimique (LIOC)." Paris 11, 1989. http://www.theses.fr/1989PA112177.
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Le laser iode-oxygène chimique est un laser susceptible de fonctionner à des puissances très élevées. Il est le seul laser chimique à transition électronique. La longueur d'onde située dans le proche infrarouge à 1,315 µm est la plus basse des lasers chimiques de haute énergie connus à ce jour. Elle correspond à la transition dipolaire magnétique I²P₁/₂ - I²P₃/₂. La source d'énergie du laser est de l'oxygène excité métastable 0₂(1 Δg) obtenu par voie chimique. La première étape de la réaction correspond à la dissociation de l'iode moléculaire suivant un mécanisme non entièrement compris. Heidner et co-auteurs ont proposé un modèle de la dissociation en deux étapes faisant intervenir une espèce intermédiaire excitée inconnue I^₂. Sur cette base, nous proposons un modèle "complet" de la dissociation où l'espèce intermédiaire excitée inconnue I*₂est identifiée aux niveaux vibrationnels de l'iode I₂(X, 30 ≤ v" ≤ 43). Les taux de réactions concernant chaque v" déterminés. Les prévisions de ce modèle sont en assez bon accord l'expérience de Heidner. Nous présentons des spectres d'excitation à haute résolution des vibrationnels de l'iode fondamental dans un mélange iode-oxygène métastable. Par inversion de spectre, en utilisant un code de minimisation approprié, nous déduisons la distribution de population en fonction de v". Les 30 ≤ v" ≤ 43 sont significativement peuplés comme le prévoit le modèle "complet". Enfin, la Diffusion Raman Anti-Stokes Cohérente (DRASC) a permis de sonder 0₂(³Σ‾g) et 0₂(¹Δg) dans un mélange iode-oxygène métastable et déterminer les concentrations des espèces et la température rotationnelle.
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Gachet, D. "Microscopie "CARS" (Coherent anti-Stokes Raman scattering). Génération du signal au voisinage d'interfaces et à l'intérieur d'une cavité Fabry-Perot." Phd thesis, 2007. http://tel.archives-ouvertes.fr/tel-00258999.
Full textAbstract:
Le processus de diffusion ``CARS'' (Coherent anti-Stokes Raman scattering) est une technique de spectroscopie qui donne accès à une information sur les modes vibrationnels intramoléculaires de l'échantillon étudié. L'introduction de ce processus de diffusion en microscopie a été pour la première fois proposée en 1982. Elle a été par la suite mise en œuvre dans une configuration colinéaire en 1999. La génération du signal en microscopie CARS a dès lors été étudiée sur des exemples simples. Dans ce mémoire de thèse, nous étendons l'analyse du signal en microscopie CARS en utilisant un formalisme purement vectoriel. En particulier, nous introduisons dans cette étude le coefficient de dépolarisation Raman du mode vibrationnel étudié et analysons son influence sur les diagrammes de rayonnement en champ lointain du signal CARS. Dans une seconde partie, nous nous intéressons à la génération du signal CARS au voisinage d'interfaces transverses et axiales. D'une part, nous présentons une méthode très simple pour obtenir des spectres CARS affranchis de tout fond non-résonant (c'est-à-dire similaires à des spectres Raman purs) au voisinage d'interfaces transverses, en utilisant une excitation conventionnelle. D'autre part, nous présentons une étude expérimentale et théorique de la modification du contraste d'une interface axiale en fonction du désaccord spectral des lasers d'excitation autour d'une résonance vibrationnelle. Ces effets sont intrinsèquement liés à la nature à la fois cohérente et résonante du processus de diffusion CARS. Enfin, dans le but de d'augmenter la sensibilité de la microscopie CARS, nous proposons de générer le signal CARS au voisinage d'une structure résonante. A cet effet, nous menons des études théorique et expérimentale de la génération du signal CARS dans une cavité Fabry-Perot. Nous démontrons des effets intéressants pour des applications en microscopie CARS, qui incluent une exaltation du signal, une augmentation de sa directivité ainsi qu'une symétrisation des signaux générés en avant et en arrière de l'objet émetteur. Cette dernière étude illustre l'influence de l'environnement électromagnétique sur la génération de lumière.
Book chapters on the topic "Conversions Stokes et anti-Stokes"
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RIGNEAULT, Hervé, and Julien DUBOISSET. "Imagerie Raman cohérente." In Spectroscopies vibrationnelles. Editions des archives contemporaines, 2020. http://dx.doi.org/10.17184/eac.4204.
Full textAbstract:
Obtenir des informations sur la matière à des échelles micrométriques, de manière non destructive et sans utiliser aucun marquage reste un défi méthodologique et technologique. Les techniques établies de microscopie de fluorescence ont permis de réelles avancées dans la compréhension des phénomènes biologiques mais le marquage utilisant des fluorophores limite considérablement cette technique, en particulier dans le domaine biomédical. Depuis une quinzaine d’année, la microscopie Raman cohérente a connu un important essor. Basée sur les propriétés vibrationnelles des molécules, cette technique permet aujourd’hui une imagerie tridimensionnelle des liaisons chimiques à cadence vidéo. De nombreux développements ont permis, à partir des concepts de la diffusion Raman et de l’optique non linéaire, d’élaborer des outils technologiques puissants permettant d’imager les échantillons biologiques en utilisant les contrastes de diffusion Raman anti-Stokes et de diffusion Raman stimulée. Dans ce chapitre, nous développons tout d’abord, grâce à des modèles simples, ces processus clés permettant d’appréhender la physique sous-jacente à l’imagerie Raman cohérente. Ensuite, nous illustrons ces techniques d’imagerie au travers de travaux menés récemment sur des échantillons biologiques et cristallins. Nous discutons enfin les perspectives actuelles concernant l’évolution des technologies et leurs domaines applicatifs.
Conference papers on the topic "Conversions Stokes et anti-Stokes"
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Auyeung, R. C. Y., D. G. Cooper, and B. J. Feldman. "Stimulated anti-Stokes Raman scattering in inverted atomic selenium." In OSA Annual Meeting. Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.tus5.
Full textAbstract:
The generation of 145.6-nm radiation by stimulated anti-Stokes Raman scattering in inverted atomic selenium was first reported by Ludewigt et al. 1 We have performed experimental studies of this process in similar excitation conditions, which allow us to compare some of the results in the two studies. The inverted population of the selenium (4p4)1S0 metastable state relative to the (4p4)3P0 state was prepared by photodissociation of COSe vapor using broadband 193-nm radiation from an ArF excimer laser. The pump beam at 205.1 nm was generated by the first-order Stokes shift in deuterium of narrowband (0.27-cm–1), 193-nm radiation from a separate, tunable ArF laser. The pump beam was tuned near the selenium (4p4)1S0–(4p35s)3P1 intermediate resonance to generate tunable, coherent radiation at 145.6 nm. We have studied the process in a variety of experimental conditions. Factors affecting the conversion efficiency and tunability include the initial COSe pressure, the intensities and relative timing of the photolyzing and pump beams, and the presence of buffer gases. The experimental results are compared with theoretical calculations based on a recently developed three-level model2 which incorporates Doppler broadening and arbitrary decay times.
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Chee, J. K., and J. M. Liu. "Parametric Frequency Conversion in a Highly Birefringent Fiber." In Nonlinear Guided-Wave Phenomena. Optica Publishing Group, 1989. http://dx.doi.org/10.1364/nlgwp.1989.thb12.
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A wide variety of nonlinear optical phenomena, such as stimulated Raman scattering[1], stimulated four-photon mixing[2], and sum-frequency generation[3], have been observed in optical fibers. For four-photon mixing in a fiber, phase matching condition has to be satisfied as well as conservation of energy. This has been successfully demonstrated both in multimode and single-mode fibers[4,5]. In a single-mode birefringent fiber, the birefringence in the fiber can compensate for the material dispersion[6,7]. Four-photon parametric process in single-mode birefringent fibers has been observed by Stolen et al. [6] when the pump polarization was along the slow axis and the Stokes and anti-Stokes pair were generated with a polarization along the fast axis with a large frequency shift. Later, Stenersen et al. [7] reported four-photon mixing with a relatively small frequency shift in highly birefringent single-mode fibers by divided pump between different polarization modes and phase-matched totally non-degenerate four-photon mixing by the pump, Stokes, and stimulated Raman Stokes to generate a new frequency. In this paper, we report the observation of various third-order nonlinear optical processes following parametric four-photon mixing in a highly birefringent fiber.
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HAHN, J. W., S. N. PARK, K. T. KANG, and S. H. CHUNG. "Measuring CO Concentration and Temperature in a CH4/air Premixed Flame with Broadband Coherent Anti-Stokes Raman Spectroscopy." In Laser Applications to Chemical Analysis. Optica Publishing Group, 1994. http://dx.doi.org/10.1364/laca.1994.wd.6.
Full textAbstract:
Coherent anti-Stokes Raman spectroscopy (CARS) has been widely used as a diagnostic tool for probing the temperature and species concentration of gas phase samples. CARS concentration measurements are typically performed either from the integration1,2 or from the shape of a CARS spectrum.3, 4 If the resonant signal of CARS is much bigger than the nonresonant background, integration of the CARS spectrum depends linearly on the squares of the concentration of the species. In practice, this method can be used to measure the concentration of major species. When the fraction of a species goes down to the order of a few percentage, the nonresonant background becomes comparable to the resonant signal of CARS and interferes with the resonant signal. In such a case, the portion of the nonresonant background included in the integration of the CARS spectrum leads to a large error in the concentration measurement. The interference of the nonresonant background and the real term of the resonant signal of CARS form modulation dips on the spectrum that are sensitive to the concentration. Recently Hahn et al.5 proposed a new technique for measuring the minor species concentration from the modulation dip of nonresonant background of broadband CARS spectrum.
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Hancock, R. D., F. R. Schauer, R. P. Lucht, V. R. Katta, and K. Y. Hsu. "CARS Temperature Measurements in a Driven Jet Diffusion Flame." In Laser Applications to Chemical and Environmental Analysis. Optica Publishing Group, 1996. http://dx.doi.org/10.1364/lacea.1996.lthd.3.
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This paper discusses the use of a broadband coherent anti-Stokes Raman scattering (CARS) system to investigate local gas temperatures during a vortex/flame interaction. The CARS system is first used to obtain flame temperature measurements in a series of near adiabatic hydrogen/air flames produced with a Hencken burner (Hencken, 1994; Hancock, et al., 1996). These temperatures are compared to adiabatic flame temperatures found using the NASA-Lewis equilibrium code (Gordon and McBride, 1976) and a computational fluid dynamics code developed by Katta, et al. (1994). These results help to validate the CARS system. Next, the CARS system is used to obtain local gas temperature measurements in an undriven hydrogen/nitrogen jet diffusion flame and during a vortex-flame interaction in the same flame, but under driven conditions. Experimental results (Hsu, et al., 1993; Carter, et al., 1995) and direct numerical simulations (Katta and Roquemore, 1995) indicate that preferential diffusion (manifest as Lewis number), acting together with flame curvature, influence the local flame temperature along the flame surface. Under certain conditions the local temperature will rise even though the flame is positively stretched-a condition which is typically thought to cause a reduction in local flame temperature. In this paper such a condition is investigated for a hydrogen/nitrogen diffusion flame using CARS and direct numerical simulations.
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Kerkvliet, Maarten, Guilherme Vaz, Nicolas Carette, and Michiel Gunsing. "Analysis of U-Type Anti-Roll Tank Using URANS: Sensitivity and Validation." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-23483.
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The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.