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Дисертації з теми "Complétude de modes quasi-Normaux"
Al, Sheikh Lamis. "Scattering resonances and Pseudospectrum : stability and completeness aspects in optical and gravitational systems." Electronic Thesis or Diss., Bourgogne Franche-Comté, 2022. http://www.theses.fr/2022UBFCK007.
Повний текст джерелаThe general context of this thesis is an effort to establish a bridge between gravitational andoptical physics, specifically in the context of scattering problems using as a guideline concepts andtools taken from the theory of non-self-adjoint operators. Our focus is on Quasi-Normal Modes(QNMs), namely the natural resonant modes of open leaky structures under linear perturbationssubject to outgoing boundary conditions. They also are referred to as scattering resonances.In the conservative self-adjoint case the spectral theorem guarantees the completeness andspectral stability of the associated normal modes. In this sense, a natural question in the non-self-adjoint setting refers to the characterization and assessment of appropriate notions of QNMcompleteness and spectral stability in open non-conservative systems. This defines the generalobjective of this thesis. To this aim, and in contrast with the traditional approach to scatter-ing resonances, we adopt a methodology in which QNMs are cast as a spectral problem of anappropriate non-self-adjoint operator. Specifically this methodology is based on following threeingredients:(i) Hyperboloidal approach: The hyperboloidal slicing approach is already used in gravitationalproblems, we introduced it here to optical ones. The idea is to study the wave equationin hyperbolic slices instead of usually used Cauchy slices. The system of coordinates ismore adapted to the problem of QNMs and its outgoing boundary conditions, in particularaddressing the exploding modes in the Cauchy approach. The modes are normalizable insuch coordinates and working in these slices eliminate the need of imposing the outgoingboundary conditions.(ii) Pseudospectrum of an operator: the notion of epsilon-pseudospectrum allows to assess the (in)stabilityof eigenvalues of an operator in the complex plane due to a perturbation to the operator oforder epsilon. This thesis introduces the notion of pseudospectrum in gravitational and opticalphysics in the vicinity of the eigenvalues.(iii) Numerical Chebyshev spectral methods: On the technical level, spectral methods providesan efficient tool when translating the problem into a numerical one. In particular we usedChebyshev basis to expand our fields.The results of this work touch three areas:(i) The instability of QNMs for some class of potentials. The fundamental modes are stablespecially under small "high frequency" perturbations, whereas overtones are sensitive tosuch perturbations. The instability of the overtones increases as their imaginary part grows.(ii) The universality of the asymptotic behaviour of QNMs and pseudospectrum. We remarkan asymptotically logarithmic behavior of pseudospectrum contour lines and bounding theopening QNMs branches from below.(iii) QNMs expansion. We revisit Lax & Phillips asymptotic resonant expansions of a "scattered field" in terms of QNMs in our physical settings. In particular , we make use of Keldysh expansion of the generalizations of the expressions for normal modes of conservative systems, specifically in terms of normalizable QNM eigenfunctions and explicit expressions for the excitation coefficients
Cognee, Kevin. "Hybridization of open photonic resonators." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0002.
Повний текст джерелаThe control of the interaction between light and matter is of paramount importance in many modern technologies, with applications ranging from sensing to telecommunication and quantum information. Nanophotonic resonators allow to enhance this interaction by the storage and confinement of the light field.This thesis studies the hybridization of eigenmodes of nano- and microresonators, and in particular the properties of hybrid resonators composed of a dielectric cavity and plasmonic nanoantennas. Due to their lossy nature, in particular radiation, photonic resonators can only be well described in the framework of quasinormal modes theory (QNM). We confirm the relevance of such theories by investigating the physics of the perturbation of high-Q dielectric cavities aided by numerical and experimental works.Then we propose a theory to study the hybridization of multiple resonators and predict the properties of the ensemble. In the context of antenna-cavity hybrids, previous works have demonstrated the great potential of such resonators to enhance light-matter interaction further than what is achieved with their components taken individually. Here we show, with theoretical and experimental works that such resonators also offer additional degrees of control over the properties of the emitted light, such as directionality or beams carrying a pure orbital angular momentum. We furthermore investigate the performances of such hybrid resonators in the context of molecular optomechanics. Indeed, we show they can be an excellent platform to enhance Raman scattering, while simultaneously offering input and output channels with controllable properties for the pump and Raman signals
Ould, El Hadj Mohamed. "Rayonnement des trous noirs en interaction avec des champs bosoniques massifs." Electronic Thesis or Diss., Corte, 2016. http://www.theses.fr/2016CORT0003.
Повний текст джерелаThis thesis focuses on the radiation from black holes interacting with massive bosonic fields (the scalar, Proca and Fierz-Pauli fields). We studied more particularly the influence of resonances spectrum (quasinormal modes or quasibound states) on the response of the black hole to an external perturbation. This work is the first step to highlight new effects in the radiation from supermassive black holes which could allow us to test the various massive gravity theories or to further support Einstein’s general relativity.More precisely:- In order to circumvent the numerous difficulties associated with massive gravity theories and black hole perturbation in this context, we worked at first on a toy model where the graviton field is replaced by a massive scalar field linearly coupled to a particle plunging into the Schwarzschild black hole. We studied the role of the field mass on the structure of the black hole responses and compared our results with those obtained for the massless field. We highlighted unexpected effects due to the mass parameter and in particular the excitation of the quasibound states of the black hole in addition to that of its quasinormal modes as well as the possible vanishing of the waveform when the particle moves on a quasi-circular trajectory.- We also considered the excitation of quasinormal modes of the Schwarzschild black hole because, from an observational point of view, they are supposed to provide a direct proof of the existence of the black holes. We have shown numerically and analytically the presence of a resonant behaviour of the quasinormal excitation factors which, theoretically, could lead to giant and slowly decaying ringings. This behaviour has been highlighted on the Fierz-Pauli field and we have generalized it to the other bosonic fields (the scalar and Proca fields). However, by working on a Cauchy problem, we also showed that, contrary to what occurs for massless fields, the quasinormal ringing cannot be clearly individualized on a waveform and its giant character is in fact neutralized due to the coexistence of two phenomena (i) the excitation of quasibound states which blur the quasinormal contribution and (ii) the evanescent nature of the particular partial modes which could excite the quasinormal modes whose excitation factor has a resonant behaviour
Lassalle, Emmanuel. "Emission quantique spontanée : modifications induites par l'environnement." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0197.
Повний текст джерелаThe control of the spontaneous emission of quantum emitters is of fundamental importance for the development of future quantum technologies. Such applications rely on the manipulation of atoms, molecules, or "artificial" atoms, as elementary sources of light, and on the exploitation of the quantum nature of the emitted light, single photons. In parallel to the recent developments in nanofabrication techniques and nanotechnologies, theoretical understanding of the fundamental interaction mechanisms between quantum emitters and their environment also becomes more and more essential.In this thesis, we tackle three different paradigms of the spontaneous emission phenomenon, all dealing with modifications of the spontaneous emission induced the environment: the problem of monitored spontaneous emission, the interaction between quantum emitters and optical resonances supported by nearby nanostructures and the remote interaction between quantum emitters and metasurfaces. We present and deal with different formalisms to model such different situations, interfacing different fields of physics like quantum optics and nanophotonics. In each of these situations, we illustrate with realistic theoretical predictions how the spontaneous emission is modified. For each case, for provide with experimental proposals for future confirmations of these predictions, to bring a better understanding and control over these fundamental processes
Faggiani, Rémi. "Resonant nanophotonics : structural slow light and slow plasmons." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0396/document.
Повний текст джерелаEnhancing light-matter interactions at micro and nanoscales is one of the spearheads of nanophotonics. Indeed, the control of the field distribution due to the resonant interaction of nanostructures with electromagnetic waves has prompted the development of numerous optical components for many applications in telecommunication, spectroscopy or sensing. A promising approach lies in the control of light speed in nanostructures. Light slowdown, obtained by wave interferences in periodic structures or subwavelength confinement in plasmonic waveguides, is associated to pulse compressions and large field enhancements,which are envisioned as key processes for the miniaturization of optical devices and the enhancement of light-matter interactions.The thesis studies both fundamental aspects and possible applications related to slow light in photonic and plasmonic nanostructures. In particular, we study the impact of periodic system sizes on the group velocity reduction and propose a novelfamily of resonators that implement slow light on very small spatial scales. We then investigate the role of fabrication disorder in slow periodic waveguides on light localization and demonstrate how modal properties influence the confinement of localized modes. Also we propose a new hollow-core photonic crystal waveguide that provides efficient and remote couplings between the waveguide and atoms thatare trapped away from it. Finally we demonstrate the important role played by slow plasmons on the emission of quantum emitters placed in nanogap plasmonic antennas and explain how large radiation efficiency can be achieved by overcoming quenching in the metal. Additionally, one part of the thesis is devoted to thederivation of a novel modal method to accurately describe the dynamics of plasmonic resonators under short pulse illumination