Ce travail de thèse est consacrée à l'étude des interractions de gaz de Bose de polaritons avec leurs environnements dans le but de déterminer l'impact de la densité, de la dimmensinalité du confinement, du potentiel ressentis par le gaz et du bain de phonons sur les propriétés du gaz de Bose.Le premier chapitre présente un condensat de polaritons unidimensionel au sein de microfils d'oxyde de zinc qui présente d'une nature quasi excitonique.En déterminant les propriétés de corrélation spatiale du gaz et en utilisant un modèle champ moyen nous déterminons l'influence combinée de la nature quasi-excitonique, du potentiel confinant et de la densité sur les propriétés de cohérence du gaz. La fin du chapitre décrit une application de ces polaritons très excitoniques à une nouvelle technique d'imagerie de Sub-longueur d'onde basée sur le concept lentilles solides à immersion.Dans la deuxième partie, nous abordons les interactions du champ de polaritons avec une caractéristique intrinsèque de l'environnement à l'état solide : les excitations thermiques du réseau appelées phonons.Dans cette partie, nous utilisons la spectroscopie Raman résolue en angle pour étudier la Fluorescence Anti-Stokes qui consiste en l'absorption d'un phonon par un état excité pour refroidir la microcavité étudiée.L'étude réalisée a exploité la fluorescence anti Stokes de polaritons en exploitant respectivement leur très courte durée de vie et leur très faible masse pour accéder à une dynamique de refroidissement extrêmement rapide rapide et une gamme d'énergie allant de 150K à 4K. / This work is devoted to the study of the interaction of a Bose gas of polariton with its environment it aims to determine the impact of the gas density, the dimensionality of the confinement, the experienced potential and the surrounding phonon bath on the polariton Bose gas characteristics.In the first chapter, we study a one dimensional polariton condensate in Zinc Oxide microwires that features a quasi excitonic nature.By determining the spatial correlation properties of the gas, and using a mean field driven dissipative model developed by our colleagues of the Laboratoire de Physique et de Mod'elisation des Milieux Condens'es we were able to determine the influence of the combined quasi excitonic nature, disordered one dimensional confining potential and density on the coherence properties of the gas. The end of the chapter describes an application of those highly excitonic polaritons to a novel subwavelength imaging technic based on the Solid Immersion Lens concept.In the second part we address the interactions of the polariton field with an intrinsic characteristic of the solid state environment : the thermal excitations of the lattice called phonons.In this part, we use angle resolved Raman spectroscopy to study Anti-Stokes Fluorescence (ASF) which consists in the the absorption of a phonon by an excited states to cool down the studied microcavity. The state of the art technics are using ion doped materials or bare excitons in semiconductors as emitters.The study performed exploited the polaritons as emitters, using respectively their very short lifetime and their very light mass to access a faster cooling dynamics and an energy range going from 150K to 4K.

O confinamento da luz em escala nanométrica, em especial para estruturas metálicas, é conferido graças à ação coletiva dos elétrons livres desses materiais que ao entrarem em ressonância com a frequência da radiação incidente geram campos intensos o suficiente para permitir que uma parcela da luz atravesse as cavidades que formam as estruturas, desafiando os limites clássicos da óptica impostos pela teoria escalar da difração. Designa-se a tal ação coletiva dos elétrons na literatura como plasmons polaritons de superfície, ou SPP da sigla em inglês para Surface Plasmon Polariton, conceito há muito estudado em Física do Estado Sólido. Porém, somente a algumas décadas com o domínio sobre a fabricação de estruturas em escala nanométrica, tornou-se possível a análise experimental e a contribuição de SPP na observação de fenômenos em nano-óptica. A ressonância de plasmons em nanoestruturas confere considerável sensibilidade ao índice de refração dos meios próximos a elas, o que abre mais um canal para estudos no campo da interação entre radiação-matéria. Dentre eles há interação de plasmons com íons de terras-raras (ITR). Estes últimos por apresentarem bandas de absorção estreitas e bem definidas, são excelentes opções como elementos na análise da interação destes com os SPPs gerados nas nanoestruturas. Uma maneira de estabelecer o contato direto entre o campo plasmônico e os ITRs é incorpora-los ao substrato no qual o filme metálico onde as nanoestruturas são fabricadas é depositado. Vidros óxidos à base de Telúrio e Germânio reúnem condições favoráveis para esse propósito, por terem alta solubilidade às terras-raras, janela de transparência relativamente larga (0,4 - 5μm) podendo ser analisados desde o visível até o infravermelho e baixa energia de fônon. O presente trabalho consistiu no esforço de criar uma plataforma para estudo direto de interações SPP com o ITR a partir da nano fabricação via técnica de feixe de íons e medir a luz emitida por processo de conversão ascendente do Érbio diretamente pela nanoestrutura devido ao decaimento do íon em SPP e na consequente remissão através da transmissão óptica extraordinária (TOE). A partir de tais medidas há fortes evidências de que a radiação emitida pelo Érbio apresenta a mesma polarização do campo plasmônico originado nas nanoestruturas. / The confinement of light at the nanoscale, especially for metallic structures is achieved due the collective action of free electrons from the material that resonate with the frequency of the incident radiation, generating enhanced fields enough to allow a portion of the light to cross the cavities that form such structures, challenging the classical limits of optics imposed by the scalar diffraction theory. Such collective action of the electrons is known in the literature as surface plasmon polariton (SPP), a concept which has already been studied in Solid State Physics, but only a few decades ago, with the development of fabrication of nanoscale structures has enabled the experimental analysis and the contribution due SPP on the observation of nanoptics phenomena. The plasmon resonance from nanostructures offers considerable sensitivity to the refractive index from the media that surround them, which opens another topic in matter-radiation interaction. There are interactions of plasmons with rare earth ions (REI). The latter class of emitters, presents narrow and well-defined absorption bands, which make them excellent options as probes to the analysis of interaction with the SPPs generated in the nanostructures. To establish direct contact between the plasmonic field and the REIs consists in embedding them into the substrate for the metallic thin film where the structures are assembled. Tellurium and Germanium oxide based glasses gather the conditions for this purpose, because they present high solubility to rare earths, a relatively wide transparency window (0.4 - 5 μm), which enables spectral analysis from visible to infrared, and low phonon energy. The present work consisted in the effort to create a direct platform to study the SPP interactions with the REI from the milling of the samples by ion beam technique; to measure the light emitted from the Erbium\'s upconversion process directly through the nanostructure due the ion decay to SPP and in the consequent remission by extraordinary optical transmission (EOT). From such measurements there are strong evidences that the radiation emitted by Erbium ions presents the same polarization from the plasmonic field originated in nanostructures.

Cette thèse présente une étude exploratoire de plusieurs aspects du couplage fort lumière-matière dans des matériaux moléculaires. Différentes propriétés héritées d’un tel couplage sont démontrées, ouvrant de nombreuses possibilités d’applications, allant du transfert d’énergie à la génération de signaux optiques non-linéaires et à l’élaboration de réseaux polaritoniques chiraux. Au travers des thématiques abordées, l’idée d’un couplage lumière-matière entrant en compétition avec les différentes fréquences de dissipation des molécules se révèle être cruciale. Ainsi, la prédominance du couplage cohérent au champ électromagnétique apparaît comme un moyen de modifier les propriétés quantiques des états moléculaires, ouvrant la voie à une nouvelle chimie des matériaux en cavité. / This thesis presents an exploratory study of several aspects of strong light-matter coupling in molecular materials. Different properties inherited from such a coupling are demonstrated, opening the way to numerous applications, ranging from energy transfer to the generation of non-linear optical signals and to the development of chiral polaritonic networks. Through the topics covered, the idea of a light-matter coupling strength competing with the different frequencies of relaxation of the molecules proves to be crucial. Thus, the predominance of the coherent coupling to the electromagnetic field appears as a new mean of modifying the quantum properties of molecular systems, opening the way to a new chemistry of materials in optical cavities.

Nous couplons des sources de rayonnement infrarouge et un spectromètre à transformée de Fourier (FTIR) avec un microscope optique en champ proche (SNOM) à pointe diffusante pour sonder les propriétés optiques locales de la matière avec une résolution spatiale sub-longueur d'onde.Nous étudions l'émission thermique de champ proche d'un échantillon constitué d'une couche d'or recouvrant partiellement du carbure de silicium, puis d'un empilement de nano-couches semi-conductrices. Nous révélons expérimentalement la présence d'ondes de surface se propageant aux différentes interfaces de ces échantillons, en imagerie et en spectroscopie. Nous sondons l'évolution spatiale du spectre de la densité locale d'états électromagnétiques grâce à l'imagerie hyperspectrale super-résolue de l'émission thermique de champ proche. Nous montrons que la résolution spatiale et le contraste entre les structures diminuent lorsque la distance à laquelle la sonde effectue les balayages augmente.Nous couplons notre SNOM et un FTIR avec le rayonnement synchrotron et démontrons la capacité d'un tel couplage de mener des études de nanospectroscopie dans l'infrarouge moyen en l'illustrant sur les échantillons précédemment mentionnés. Nous démontrons l'imagerie térahertz super-résolue à l'aide du rayonnement synchrotron.Nous étudions expérimentalement l'influence de l'illumination sur les images obtenues en SNOM et montrons que la détection de l'émission thermique de champ proche permet d'obtenir des images exemptes de distorsions et donc plus simples à interpréter que celles obtenues en utilisant un laser monochromatique ou l'émission thermique de champ lointain. Nous développons un mode d'imagerie 3D. / We couple infrared sources with a scattering near-field scanning optical microscope (SNOM) combined with a Fourier transform infrared spectrometer (FTIR) in order to probe the local optical properties of matter with sub-wavelength spatial resolution. We study the near-field thermal emission of a surface made of silicon carbide and gold, and then of a semiconductor-based multilayer. We reveal experimentally the presence of surface waves propagating at the different interfaces of these samples, by imaging and spectroscopy. We probe the spatial evolution of the electromagnetic local density of states spectrum thanks to super-resolved hyperspectral imaging of the near-field thermal emission. We show that spatial resolution and contrast between the structures decrease as the distance at which the probe performs the scans increases. We couple our SNOM and FTIR with synchrotron radiation and demonstrate the capability of such coupling to perform nanospectroscopy studies in the mid-infrared range by investigating the samples mentioned above. We demonstrate super-resolved terahertz imaging using synchrotron radiation. We experimentally study the influence of the illumination on the images obtained in SNOM and show that the detection of the near-field thermal emission provides distortion-free images and therefore are easier to interpret than those obtained using a monochromatic laser source or far-field thermal emission. We also develop a 3D imaging technique.

Dans cette thèse, nous étudions les propriétés optiques d'un système multicouche (air-Au-SiO₂-Au-Ti-verre). Les interfaces sont planes et la modélisation est réalisée en utilisant les coefficients de Fresnel à l'interface et la propagation d'ondes planes dans les couches. Deux modèles sont utilisés où l'échantillon est : i) excité par une source à l'infini ; ii) excité par une source locale. Dans l'expérience que nous avons modélisée l'empilement est excité par les électrons tunnel inélastiques dans un microscope à effet tunnel (STM). Dans le modèle, le courant tunnel inélastique est remplacé par un dipôle oscillant vertical. En utilisant ces modèles, nous avons calculé les flux réfléchis (reflectance) et transmis (transmittance) d'une source de lumière à l'infini et le flux transmis de l'excitation locale. La reflectance, transmittance et le flux transmis montrent des modes plasmoniques (surface plasmon polaritons (SPP)) et photoniques (guide d'onde (WG)). A des longueurs d'onde particulières, les courbes de dispersion des SPP et WG présentent un croisement évité. Le choix des épaisseurs d'or et de silice a deux contraintes: une amplitude importante des observables et une large dépendance en longueurs d'onde du vecteur d'onde dans le plan. Nous étudions aussi l'influence des épaisseurs sur les observables. Nous avons trouvé que les observables ont des amplitudes importantes à pour une épaisseur d'or de [10, 90 nm] pour l'empilement de trois couches et de [10, 50 nm] pour celui de six couches. Les modes de guide d'onde apparaissent pour une épaisseur de la couche de silice de >190 nm. Afin de caractériser la localisation du champ dans l'empilement et déterminer la nature du mode, nous avons calculé le champ électrique en fonction de la coordonnée de pénétration z. Nous avons trouvé que pour le mode SPP le champ est localisé à l'interface Au-air, tandis que le champ électrique du guide d'onde est confiné dans la couche de silice. Les résultats théoriques présentés sont en bon accord avec les résultats des études expérimentales menées dans notre groupe. / In this thesis, we investigate the optical properties of a six-layer stack (air-Au-SiO₂-Au-Ti-glass). The interfaces are flat and the modeling is performed using elementary Fresnel expressions at the interface and plane wave propagation in the layers. Two models are used where the sample is: i) excited by a source at infinity (excitation by source at infinity (ESI)); ii) excited by a local source. In the experiments we are modeling this source consists of the inelastic tunneling electrons from a scanning tunneling microscope (STM). In our modeling this source is replaced by a vertical oscillating dipole. Using these two models one calculates the reflected (reflectance) and the transmitted (transmittance) flux from a source at infinity and the transmitted flux of a local source. Surface plasmon polariton (SPP) and wave guide (WG) modes may be identified in the reflectance, transmittance and transmitted flux. In a particular wavelength domain the SPP and WG repel each other giving rise to an avoided crossing. The choice of the gold (Au) and silica (SiO₂) thicknesses of the six-layer stack is guided by two requirements: high amplitude of the observable and wide wavelength dependence of the in-plane wave vector. We also study the influence of the gold and silica thicknesses on the observables. We find that the observables are significant for dAu[10, 90 nm] for the three and dAu[10, 50 nm] for six layer stacks and this predictive study guided the choice of the experimental sample thicknesses. The wave guide mode appears for dSiO₂ >190 nm. The electric field as a function of the penetration coordinate z is calculated in order to characterize the location of the field in the stack and to assign the nature of the modes. We observe that for the SPP the electric field is confined at the Au-air interface whereas, the electric fields corresponding to the WG mode are confined inside SiO₂ layer. Our calculations presented in this work are in good agreement with the experimental measurements performed in our group.

Diese Arbeit beschäftigt sich mit der Untersuchung der starken Kopplung und Laseremission in Strukturen, die ZnO, ZnCdO oder organische Moleküle als aktives Material enthalten. Die ZnCdO basierten Vielfachquantengräben erreichen ihre Laserschwelle durch optische Ruckkopplung an streuenden Luftlöchern. Diese Emitter nennt man random laser. Die Dynamik ihrer Emission unter quasi-stationären Bedingungen ist der hier gezeigte Fokus. Hoch reproduzierbare Anregungen werden verwendet um sowohl die Dynamik eines einzelnen Beschusses aber auch die Unterschiede verschiedener Anregungen zu untersuchen. Die experimentellen Daten werden durch numerische Simulation qualitativ reproduziert und mit Methoden der Netzwerktheorie interpretiert. Die verbreitetere optische Rückkopplung durch einen Resonator wird in der Untersuchung des Moleküls L4P und seiner Spiro-derivate benutzt. Zwei identische Braggspiegel umschließen die aktive Schicht aus L4P-SP2, das in eine Polymermatrix eingebettet ist, eine Dicke von 12 Mikrometer hat und in einer einzelnen Mode lasert (schwache Kopplung). Durch Verringerung der aktiven Schicht auf die Hälfte der Resonanzwellenlänge wird das System in den Bereich der starken Kopplung gebracht. Eine Rabi-Aufspaltung von 90 meV wird zu beiden vibronischen Resonanzen beobachtet. Die energetische Position in Resonanz zu ZnO macht dieses Molekül zu einem guten Kandidaten für die Fertigung einer hybriden Mikrokavität im Bereich der starken Kopplung. Dies wurde in einer teilweise epitaktisch gewachsenen Mikrokavität angewandt, die aus einem ZnMgO basierten Braggspiegel und sechs Quantengräben besteht. Darauf folgt eine aufgeschleuderte Schicht von L4P in der Polymermatrix. Der Resonator wird mit einem dielektrischen Spiegel fertiggestellt. Tieftemperatur Reflektion zeigt eine deutlichen ausweichen und eine gleichverteilte Mischung der drei Resonanz im mittleren Polaritonzweig. / This thesis presents the investigation of strong coupling and lasing in structures using ZnO, ZnCdO or organic molecules as active material. The ZnCdO based multi quantum well structures reach the lasing threshold by using scattering at air holes as the optical feedback. Such emitters are called random lasers. The dynamics of their emission under quasi-stationary condition is the point of interest presented. Highly reproducible excitations are used to investigate the single shot dynamics and their shot to shot differences. The experimental data is qualitatively reproduced by numerical simulation and interpreted by means of network theory. The more common optical feedback by a cavity is applied in the investigation of the molecule L4P and its spiro-derivatives. Using two identical SiO2/ZrO2 based Bragg reflectors surrounding an active layer of L4P-SP2 in a polymer matrix of approximately 12 microns thickness reached single mode lasing (weak coupling). Reducing the active layer thickness to half the resonance wavelength pushes the system into the strong coupling regime. Angular resolved reflectivity shows the anticrossing of the tuned cavity resonance to two vibronic transitions of the molecule. The Rabi-splitting to both vibronic resonances reaches around 90 meV. The energetic position in resonance to ZnO makes this molecule a promising candidate for a hybrid inorganic/organic microcavity in the strong coupling regime. This is used in a partially epitaxially grown microcavity composed of a ZnMgO based Bragg reflector (alternating layers of different Mg content) and six quantum wells. This is followed by a spincoated layer of L4P in a polymer matrix. The cavity is finished by a dielectric mirror. Low temperature reflectivity shows a clear anticrossing reaching an equal mixing of all resonances for the middle branch.

Die vorliegende Dissertation befasst sich mit der ramanspektroskopischen Charakterisierung von Galliumnitrid (GaN). Der Zusammenhang zwischen Waferkrümmung und mechanischer Restspannungen wird diskutiert. Mit Hilfe konfokaler Mikro-Ramanmessungen wurden Dotierprofile nachgewiesen sowie die Ladungsträgerkonzentration und -beweglichkeit ermittelt. Sämtliche Ramantensorelemente von wz-GaN wurden erstmals durch die Anwendung verschiedener Streugeometrien bestimmt. Eine neu entwickelte Vorwärtsstreuanordnung ermöglichte die Beobachtung von Phonon-Polaritonen. Es konnte gezeigt werden, dass von der theoretischen und experimentellen Betrachtung der Ramanstreuintensitäten dieser Elementaranregungen eindeutig das Vorzeichen der Faust-Henry-Koeffizienten von wz-GaN abgeleitet werden kann. Im Rahmen dieser Arbeit wurden alle Faust-Henry-Koeffizienten für GaN experimentell bestimmt. / This thesis focuses on special aspects of the Raman spectroscopical characterization of wurtzite gallium nitride (wz-GaN). The correlation between wafer curvature and residual stress is discussed. By means of confocal micro-Raman measurements doping profiles were detected as well as the density and mobility of free charge carriers were deduced. All Raman scattering cross sections of wz-GaN were determined the first time using different scattering configurations. A novel method for near-forward scattering was developed in order to observe phonon polaritons with pure symmetry. It is shown that the theoretical and experimental consideration of the Raman scattering efficiency of these elementary excitations allow for determining the sign of the Faust-Henry coefficients of wz-GaN unambiguously. The Faust-Henry coefficients of GaN were deduced from Raman scattering efficiencies of corresponding TO and LO phonons.

Die vorliegende Arbeit behandelt den Einfluss eines Defekt-induzierten, intrinsischen, statischen Unordnungspotentials innerhalb einer planaren, ZnObasierten Mikrokavität (MK) auf die lokale Dichteverteilung eines darin erzeugten, dynamischen Exziton-Polariton Bose-Einstein-Kondensats (BEK). Dies ist von Interesse, da die derzeitigen, z.B. GaN- oder ZnO-basierten MK, welche die Erzeugung von Exziton-Polariton BEKs bei Raumtemperatur ermöglichen und daher für zukünftige Anwendungen in realen Bauelementen geeignet erscheinen, durch eine hohe Defektdichte gekennzeichnet sind. Mit Hilfe eines eigens dafür aufgebauten Michelson-Interferometers wurde die Kohärenzzeit des Exziton-Polariton BEKs ermittelt, welche die Lebenszeit der einzelnen, unkondensierten Polaritonen um einen Faktor 140 übersteigt. Somit konnte das untersuchte, quantenmechanische System als zeitlich koh ärentes Kondensat identifiziert werden, da die Kohärenz während des stetigen Zerfalls und der Neubildung der einzelnen Polaritonen erhalten bleibt. Weiterhin wurden durch Unordnung hervorgerufene Dichtefluktuationen innerhalb des Polariton-Kondensats untersucht, welche in Form von Intensitäts- Fluktuationen in der Fernfeldverteilung der BEK-Emission beobachtet wurden. Dazu wurde der experimentelle Datensatz einer anregungsleistungsabhängigen Photolumineszenzuntersuchung analysiert. Dabei wurde festgestellt, dass die beobachteten Intensitätsfluktuationen über einen großen Anregungsleistungsbereich stabil bleiben, und zwar bis zum 20-fachen Wert der Schwellenleistung, welche für die Erzeugung des Polariton-BEKs nötig ist. Dies deutet auf eine gleichbleibende, durch Unordnung hervorgerufene, lokale Dichtevariation des BEKs trotz steigender Gesamtteilchendichte hin, was im starken Widerspruch zum theoretisch vorausgesagtem und experimentell gefundenem Verhalten von Kondensaten im thermischen Gleichgewicht steht. Die hier vorliegenden experimentellen Befunde konnten anhand eines Vergleichs mit numerischen Simulationen, basierend auf einem neu entwickelten theoretischem Modell, auf das Zusammenspiel des vorliegenden Unordnungspotentials und des Nicht-Gleichgewichtscharakters der untersuchten Exziton-Polariton Kondensate zurückgeführt werden. Dies verursacht dichteunabhängige Phasenfluktuationen innerhalb des Kondensats, welche die beobachteten Fluktuationen in der Fernfeldverteilung der Emission hervorrufen.:1 Introduction 1 2 Physical Basics 9 2.1 Distributed Bragg Reflectors (DBRs) . . . . . . . . . . . . . . . 10 2.2 Microcavities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3 Light-Matter-Coupling . . . . . . . . . . . . . . . . . . . . . . . 14 2.3.1 Weak Coupling Regime (WCR) . . . . . . . . . . . . . . 15 2.3.2 Strong Coupling Regime (SCR) . . . . . . . . . . . . . . 16 2.4 Bose-Einstein Condensation . . . . . . . . . . . . . . . . . . . . 19 2.4.1 Mean-Field Description . . . . . . . . . . . . . . . . . . . 21 2.4.2 Review of Research on Disorder Effects on Polariton Condensates . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.5 Coherence Properties . . . . . . . . . . . . . . . . . . . . . . . . 29 2.5.1 Ideal Light Source . . . . . . . . . . . . . . . . . . . . . 30 2.5.2 Real Light Source . . . . . . . . . . . . . . . . . . . . . . 33 2.5.3 Wiener-Khinchin Theorem (WKT) . . . . . . . . . . . . 36 I Experimental Observations 39 3 The ZnO-based Microcavity - Review of the known Properties 41 3.1 Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.1.1 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.1.2 Microstructure . . . . . . . . . . . . . . . . . . . . . . . 44 3.2 Bose-Einstein Condensation of Exciton-Polaritons . . . . . . . . 45 3.3 Conclusion and remaining Problems . . . . . . . . . . . . . . . . 52 4 Coherence Spectroscopy 53 4.1 Micro-Photoluminescence Setup . . . . . . . . . . . . . . . . . . 53 i 4.1.1 Excitation Sources . . . . . . . . . . . . . . . . . . . . . 57 4.1.2 Detection Units . . . . . . . . . . . . . . . . . . . . . . . 58 4.2 Michelson Interferometer . . . . . . . . . . . . . . . . . . . . . . 60 4.2.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . 60 4.2.2 Determination of First Order Correlation Function . . . . 62 4.3 Performance of the Interferometer . . . . . . . . . . . . . . . . . 66 5 Experimental Characterization of Bose-Einstein Condensates 69 5.1 Threshold Power Density for Polariton Condensation . . . . . . 70 5.2 Determination of Coherence Time . . . . . . . . . . . . . . . . . 78 5.3 Inhomogeneous Emission Profile . . . . . . . . . . . . . . . . . . 85 5.3.1 Analysis of individual Energy Branches . . . . . . . . . . 85 5.3.2 Origin of disorder potential . . . . . . . . . . . . . . . . 93 5.4 Summary of Experimental Results . . . . . . . . . . . . . . . . . 102 II Theoretical Predictions 105 6 Disorder Effects on an equilibrium BEC 109 7 Overview of the Theoretical Analysis of quasi-equilibrium and non-equilibrium BEC 113 7.1 Model for extended Gross-Pitaevskii equation including Gain and Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 7.2 Disorder Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 8 Numerical Simulations 125 8.1 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 8.2 Choice of Parameters . . . . . . . . . . . . . . . . . . . . . . . . 126 8.3 Results for both Scenarios . . . . . . . . . . . . . . . . . . . . . 130 8.4 Comparison with Experimental Data . . . . . . . . . . . . . . . 132 9 Summary of Part II 139 III Summary and Outlook 141 A Appendix 149 A.1 Alignment Procedure for the Michelson Interferometer . . . . . 149 A.2 Performance of the Interferometer . . . . . . . . . . . . . . . . . 152 A.2.1 Methods and Concepts . . . . . . . . . . . . . . . . . . . 153 A.2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 A.2.3 Impact of Experimental Artifacts . . . . . . . . . . . . . 175 A.3 Impact of Noise on the evaluated Visibility . . . . . . . . . . . . 182 A.4 FFT Analysis of Far-Field BEC Emission Pattern . . . . . . . . 185 Acknowledgement 203 Curriculum vitae 205 declaration 206 List of own and contributed articles 207

Plasmonic nanostructures provide unique opportunities to improve the detection limits of chiroptical spectroscopies by enhancing chiral light-matter interactions. The most significant of such interaction occur in ultraviolet (UV) range of the electromagnetic spectrum that remains challenging to access by conventional localized plasmon resonance based sensors. Although Surface Plasmon Polaritons (SPPs) on noble metal films can sustain resonances in the desired spectral range, their transverse magnetic nature has been an obstacle for enhancing chiroptical effects. We demonstrate, both analytically and numerically, that SPPs excited by near-field sources can exhibit rich and non-trivial chiral characteristics. In particular, we show that the excitation of SPPs by a chiral source not only results in a locally enhanced optical chirality but also achieves manifold enhancement of net optical chirality. Our finding that SPPs facilitate a plasmonic enhancement of optical chirality in the UV part of the spectrum is of great interest in chiral bio-sensing. Next we focus on the new concepts of transverse spin angular momentum and Belinfante spin momentum of evanescent waves, which have recently drawn considerable attention. We investigate these novel physical properties of electromagnetic fields in the context of chiral surface plasmon polaritons. We demonstrate, both analytically and numerically, that locally excited surface plasmon polaritons possess transverse Spin angular momentum and Belinfante momentum with rich and non-trivial characteristics. We also show that the transverse spin angular momentum of locally excited surface plasmon polaritons leads to the emergence of transverse chiral forces in opposite directions for chiral objects of different handedness. The magnitude of such a transverse force is comparable to the optical gradient force and scattering forces. This finding may pave the way for realization of optical separation of chiral biomolecules

Exciton-polaritons are the fundamental excitations arising from the strong coupling of quantum well excitons and cavity photons in semiconductor microcavities. They are compound bosons for which stimulated scattering and macroscopic occupation of single quantum states can occur at sufficiently high densities. One way of creating such polariton condensates is with nonresonant optical pumping. Doing so creates a large density of free- carriers and excitons that strongly interact and blueshift the polariton energy levels. Using spatially patterned nonresonant fields, the polariton potential landscape can be tailored and optically trapped condensates can be created. This thesis shows that the spin properties of polariton condensates are strongly modified by such trapping. Under linearly polarised pumping, helicity can spontaneously develop at a critical occupation, breaking the parity symmetry. This formation of spin-up/spin-down condensates is explained within a Gross-Pitaevskii model which accurately reproduces the influence of electric fields and condensate density. Under elliptically polarised pumping, two phenomena are observed: the formation of condensates with the opposite handedness to the pump and hysteresis of both occupation and spin with respect to pump power. The spatial dependence of these effects highlights the limitations of commonly used models of polariton condensation. Finally, the suitability of patterned optical fields for the creation of polariton lattices is explored. For small chains of condensates, controllable coupling between adjacent spins is demonstrated, with the formation of antiferromagnetic and ferromagnetic domains. The extent of these domains is strongly affected by sample nonuniformity, fundamentally limiting the scalability of these lattices.