Fundamentals and applications of spatial dissipative solitons in photonic devices : [Chapter 6]

We review the properties of optical spatial dissipative solitons (SDS). These are stable, self‐localized optical excitations sitting on a uniform, or quasi‐uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed, in optics they are often termed “cavity solitons.” We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor‐based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, for example in all‐optical delay lines

Theoretical approach to atomic-scale nanoplasmonics as probed by light and swift electrons

223 P.This thesis tackles the theoretical description of atomic-scale features in plasmonic nanostructures asprobed by light and swift electrons. Plasmonic nanostuctures are known to localize and enhanceelectromagnetic fields in their proximity, and thus serve as building blocks to perform improved andenhanced molecular spectroscopy on them. We focus on the analysis of the effect of atomic-scale featuresin the overall response of plasmonic nanoparticles and nanocavities. We apply ab initio atomisticquantum time-dependent density functional theory (TDDFT) to unveil the near-field distribution aroundmetallic antennas, and describe "classically" various atomic-scale features such as continuous protrusionson the surfaces of the metal using a Boundary Element Method (BEM), providing an extra localization ofthe field. Moreover, we propose an analytical model to address the signal increase observed in surfaceenhancedRaman scattering (SERS) spectra related to local variations of the electron density associated toatomic-scale defects. Last, we identify the excitation of confined bulk plasmons (CBP) within theTDDFT calculations for the electron energy loss (EEL) probability of atomistic clusters, and provide asemi-analytical expression within a Hydrodynamic Model (HDM) to address such excitation

Etats localisés dans les systèmes fluides : application à la double diffusion

Les états spatialement localisés sont des solutions physiques possédant une structure spatiale particulière en une région bien définie d'un domaine structuré différemment. Nous nous intéressons aux états spatialement localisés susceptibles de se former lorsqu'une convection d'origine thermique est couplée à une convection d'origine solutale ou induite par la rotation du système. Trois configurations physiques différentes sont abordées : la convection de double diffusion induite par des gradients thermiques et solutaux verticaux dans des couches fluides bidimensionnelles, celle induite par des gradients horizontaux dans des cavités tridimensionnelles et la convection de Rayleigh-Bénard en présence de rotation. Dans chacun des cas, des solutions spatialement localisées sont obtenues et analysées en utilisant la théorie des systèmes dynamiques. Les résultats obtenus dans ce travail révèlent différents scénarios d'un même mécanisme baptisé snaking, observé et analysé è l'aide d'équations modèles.Spatially localized states are physical solutions with a particular structure in a well-defined region in space that is embedded in a different background. We focus here on such states that are formed when thermal convection is coupled to solutal or Coriolis forcing. Three different physical configurations are studied: doubly diffusive convection with vertical gradients of temperature and concentration in two-dimensional fluid layers, doubly diffusive convection with horizontal gradients in three-dimensional fluid layers and Rayleigh-Bénard convection in the presence of rotation. In each of these cases, spatially localized solutions are computed and analyzed using dynamical systems theory. Our results reveal different variations of snaking, a mechanism observed and analyzed using model equations

Theoretical approach to atomic-scale nanoplasmonics as probed by light and swift electrons

223 P.This thesis tackles the theoretical description of atomic-scale features in plasmonic nanostructures asprobed by light and swift electrons. Plasmonic nanostuctures are known to localize and enhanceelectromagnetic fields in their proximity, and thus serve as building blocks to perform improved andenhanced molecular spectroscopy on them. We focus on the analysis of the effect of atomic-scale featuresin the overall response of plasmonic nanoparticles and nanocavities. We apply ab initio atomisticquantum time-dependent density functional theory (TDDFT) to unveil the near-field distribution aroundmetallic antennas, and describe "classically" various atomic-scale features such as continuous protrusionson the surfaces of the metal using a Boundary Element Method (BEM), providing an extra localization ofthe field. Moreover, we propose an analytical model to address the signal increase observed in surfaceenhancedRaman scattering (SERS) spectra related to local variations of the electron density associated toatomic-scale defects. Last, we identify the excitation of confined bulk plasmons (CBP) within theTDDFT calculations for the electron energy loss (EEL) probability of atomistic clusters, and provide asemi-analytical expression within a Hydrodynamic Model (HDM) to address such excitation

Principles and theory of protein-based pattern formation

Biological systems perform functions by the orchestrated interplay of many small components without a "conductor." Such self-organization pervades life on many scales, from the subcellular level to populations of many organisms and whole ecosystems. On the intracellular level, protein-based pattern formation coordinates and instructs functions like cell division, differentiation and motility. A key feature of protein-based pattern formation is that the total numbers of the involved proteins remain constant on the timescale of pattern formation. The overarching theme of this thesis is the profound impact of this mass-conservation property on pattern formation and how one can harness mass conservation to understand the underlying physical principles. The central insight is that changes in local densities shift local reactive equilibria, and thus induce concentration gradients which, in turn, drive diffusive transport of mass. For two-component systems, this dynamic interplay can be captured by simple geometric objects in the (low-dimensional) phase space of chemical concentrations. On this phase-space level, physical insight can be gained from geometric criteria and graphical constructions. Moreover, we introduce the notion of regional (in)stabilities, which allows one to characterize the dynamics in the highly nonlinear regime reveals an inherent connection between Turing instability and stimulus-induced pattern formation. The insights gained for conceptual two-component systems can be generalized to systems with more components and several conserved masses. In the minimal setting of two diffusively coupled "reactors," the full dynamics can be embedded in the phase-space of redistributed masses where the phase space flow is organized by surfaces of local reactive equilibria. Building on the phase-space analysis for two component systems, we develop a new approach to the important open problem of wavelength selection in the highly nonlinear regime. We show that two-component reaction–diffusion systems always exhibit uninterrupted coarsening (the continual growth of the characteristic length scale) of patterns if they are strictly mass conserving. Selection of a finite wavelength emerges due to weakly broken mass-conservation, or coupling to additional components, which counteract and stop the competition instability that drives coarsening. For complex dynamical phenomena like wave patterns and the transition to spatiotemporal chaos, an analysis in terms of local equilibria and their stability properties provides a powerful tool to interpret data from numerical simulations and experiments, and to reveal the underlying physical mechanisms. In collaborations with different experimental labs, we studied the Min system of Escherichia coli. A central insight from these investigations is that bulk-surface coupling imparts a strong dependence of pattern formation on the geometry of the spatial confinement, which explains the qualitatively different dynamics observed inside cells compared to in vitro reconstitutions. By theoretically studying the polarization machinery in budding yeast and testing predictions in collaboration with experimentalists, we found that this functional module implements several redundant polarization mechanisms that depend on different subsets of proteins. Taken together, our work reveals unifying principles underlying biological self-organization and elucidates how microscopic interaction rules and physical constraints collectively lead to specific biological functions.Biologische Systeme führen Funktionen durch das orchestrierte Zusammenspiel vieler kleiner Komponenten ohne einen "Dirigenten" aus. Solche Selbstorganisation durchdringt das Leben auf vielen Skalen, von der subzellulären Ebene bis zu Populationen vieler Organismen und ganzen Ökosystemen. Auf der intrazellulären Ebene koordiniert und instruieren proteinbasierte Muster Funktionen wie Zellteilung, Differenzierung und Motilität. Ein wesentliches Merkmal der proteinbasierten Musterbildung ist, dass die Gesamtzahl der beteiligten Proteine auf der Zeitskala der Musterbildung konstant bleibt. Das übergreifende Thema dieser Arbeit ist es, den tiefgreifenden Einfluss dieser Massenerhaltung auf die Musterbildung zu untersuchen und Methoden zu entwickeln, die Massenerhaltung nutzen, um die zugrunde liegenden physikalischen Prinzipien von proteinbasierter Musterbildung zu verstehen. Die zentrale Erkenntnis ist, dass Änderungen der lokalen Dichten lokale reaktive Gleichgewichte verschieben und somit Konzentrationsgradienten induzieren, die wiederum den diffusiven Transport von Masse antreiben. Für Zweikomponentensysteme kann dieses dynamische Wechselspiel durch einfache geometrische Objekte im (niedrigdimensionalen) Phasenraum der chemischen Konzentrationen erfasst werden. Auf dieser Phasenraumebene können physikalische Erkenntnisse durch geometrische Kriterien und grafische Konstruktionen gewonnen werden. Darüber hinaus führen wir den Begriff der regionalen (In-)stabilität ein, der es erlaubt, die Dynamik im hochgradig nichtlinearen Regime zu charakterisieren und einen inhärenten Zusammenhang zwischen Turing-Instabilität und stimulusinduzierter Musterbildung aufzuzeigen. Die für konzeptionelle Zweikomponentensysteme gewonnenen Erkenntnisse können auf Systeme mit mehr Komponenten und mehreren erhaltenen Massen verallgemeinert werden. In der minimalen Fassung von zwei diffusiv gekoppelten "Reaktoren" kann die gesamte Dynamik in den Phasenraum umverteilter Massen eingebettet werden, wobei der Phasenraumfluss durch Flächen lokaler reaktiver Gleichgewichte organisiert wird. Aufbauend auf der Phasenraumanalyse für Zweikomponentensysteme entwickeln wir einen neuen Ansatz für die wichtige offene Fragestellung der Wellenängenselektion im hochgradig nichtlinearen Regime. Wir zeigen, dass "coarsening" (das stetige wachsen der charakteristischen Längenskala) von Mustern in Zweikomponentensystemen nie stoppt, wenn sie exakt massenerhaltend sind. Die Selektion einer endlichen Wellenlänge entsteht durch schwach gebrochene Massenerhaltung oder durch Kopplung an zusätzliche Komponenten. Diese Prozesse wirken der Masseumverteilung, die coarsening treibt, entgegen und stoppen so das coarsening. Bei komplexen dynamischen Phänomenen wie Wellenmustern und dem Übergang zu raumzeitlichen Chaos bietet eine Analyse in Bezug auf lokale Gleichgewichte und deren Stabilitätseigenschaften ein leistungsstarkes Werkzeug, um Daten aus numerischen Simulationen und Experimenten zu interpretieren und die zugrunde liegenden physikalischen Mechanismen aufzudecken. In Zusammenarbeit mit verschiedenen experimentellen Labors haben wir das Min-System von Escherichia coli untersucht. Eine zentrale Erkenntnis aus diesen Untersuchungen ist, dass die Kopplung zwischen Volumen und Oberfläche zu einer starken Abhängigkeit der Musterbildung von der räumlichen Geometrie führt. Das erklärt die qualitativ unterschiedliche Dynamik, die in Zellen im Vergleich zu in vitro Rekonstitutionen beobachtet wird. Durch die theoretische Untersuchung der Polarisationsmaschinerie in Hefezellen, kombiniert mit experimentellen Tests theoretischer Vorhersagen, haben wir herausgefunden, dass dieses Funktionsmodul mehrere redundante Polarisationsmechanismen implementiert, die von verschiedenen Untergruppen von Proteinen abhängen. Zusammengenommen beleuchtet unsere Arbeit die vereinheitlichenden Prinzipien, die der intrazellulären Selbstorganisation zugrunde liegen, und zeigt, wie mikroskopische Interaktionsregeln und physikalische Bedingungen gemeinsam zu spezifischen biologischen Funktionen führen

Plasmons in nanoparticles: atomistic Ab Initio theory for large systems

205 p.El trabajo realizado en esta tesis doctoral se centra en la implementación de nuevos algoritmos y de suaplicación en diferentes tipos de nanoestructuras. El programa científico en el que se han llevado a cabolas extensiones es una implementación eficiente de la teoría funcional de densidad dependiente deltiempo, conocida como MBPT-LCAO.Las principales extensiones realizadas son las siguientes: implementación de la espectroscopía de pérdidade energía de electrones en el espacio real, mejora del procedimiento iterativo para permitir cálculos degran tamaño sin precedentes, cálculo del campo eléctrico inducido e implementación de la espectroscopíade dispersión Raman.Estas implementaciones se han utilizado en agregados y agregados dímeros de sodio y plata, así como ennanotubos de carbono y nitruro de boro. Se han calculado tanto el espectro de absorción como los camposeléctricos inducidos para todos estos sistemas. De esta forma, este trabajo nos ha permitido entendermejor la respuesta de tales nanoestructuras bajo la influencia de una perturbación externa

Developing novel nonlinear materials for metaphotonics device applications

Recent advancements in flat-optics, metamaterials research, and integrated optical devices have established the need for more efficient, spectrally tunable, and Si-compatible optical media and nanostructures with designed linear/nonlinear responses that can enable high-density integration of ultrafast photonic-plasmonic functionalities on the chip. Traditional methodologies for nanoscale photon manipulation utilize lossy materials, such as noble metals, which lack significant optical tunablility and compatibility with complementary metal-oxide-semiconductor technologies. In this dissertation, we propose, develop, and characterize alternative plasmonic materials that overcome these limitations while providing novel opportunities for significant optical nonlinear enhancement. Specifically, we investigate the plasmonic resonant regime and the nonlinear optical responses of Si- and O2- doped titanium nitride, SiO2- doped indium oxide, and Sn-doped indium oxide with engineered structural and optical dispersion behavior. We study a number of novel passive metaphotonic devices that leverage refractive index control in low-loss materials for near-field engineering and nanoscale nonlinear optical enhancement. Moreover, we integrate the developed alternative plasmonic materials into active metaphotonic surfaces for electro-optical modulation, enhanced light absorption, and ultrafast photon detection. Furthermore, utilizing the double-beam accurate Z-scan technique, we characterize the intrinsic nonlinear susceptibility χ(3) of optical nanolayers with epsilon-near-zero behavior as a function of their microstructural properties that we largely control by post-deposition annealing. A main objective of this work is to establish robust structure-property relationships for the control of optical dispersion, Kerr nonlinearity, and near-field resonances that extend from the visible to the infrared. This work substantially expands and diversifies the reach of plasmonics, flat-optics, and nonlinear optics across multiple spectral regions within scalable and Si-compatible novel material platforms

DFT exchange: sharing perspectives on the workhorse of quantum chemistry and materials science

In this paper, the history, present status, and future of density-functional theory (DFT) is informally reviewed and discussed by 70 workers in the field, including molecular scientists, materials scientists, method developers and practitioners. The format of the paper is that of a roundtable discussion, in which the participants express and exchange views on DFT in the form of 302 individual contributions, formulated as responses to a preset list of 26 questions. Supported by a bibliography of 777 entries, the paper represents a broad snapshot of DFT, anno 2022