Explicit Determination of Pinned-Pinned Beams with a Finite Number of Given Buckling Loads

We present an analytical procedure for the exact, explicit construction of Euler-Bernoulli beams with given values of the first N buckling loads. The result is valid for pinned-pinned (P-P) end conditions and for beams with regular bending stiffness. The analysis is based on a reduction of the buckling problem to an eigenvalue problem for a vibrating string, and uses recent results on the exact construction of Sturm-Liouville operators with prescribed natural frequencies

Whispering gallery quantum well exciton polaritons in an Indium Gallium Arsenide microdisk cavity

Despite appealing high-symmetry properties that enable high quality factor and strong confinement, whispering gallery modes of spherical and circular resonators have been absent from the field of quantum-well exciton polaritons. Here we observe whispering gallery exciton polaritons in a Gallium Arsenide microdisk cavity filled with Indium Gallium Arsenide quantum wells, the testbed materials of polaritonics. Strong coupling is evidenced in photoluminescence and resonant spectroscopy, accessed through concomitant confocal microscopy and near-field optical techniques. Excitonic and optical resonances are tuned by varying temperature and disk radius, revealing Rabi splittings between 5 and 10 meV. A dedicated analytical quantum model for such circular polaritons is developed, which reproduces the measured values. At high power, lasing is observed and accompanied by a blueshift of the emission that points to the regime of polariton lasing

Efficient optical coupling to gallium arsenide nano-waveguides and resonators with etched conical fibers

We explore new methods for coupling light to on-chip gallium arsenide nanophotonic structures using etched conical optical fibers. With a single-sided conical fiber taper, we demonstrate efficient coupling to an on-chip photonic bus waveguide in a liquid environment. We then show that it is possible to replace such on-chip bus waveguide by two joined conical fibers in order to directly couple light into a target whispering gallery disk resonator. This latter approach proves compliant with demanding environments, such as a vibrating pulse tube cryostat operating at low temperature, and it is demonstrated both in the telecom band and in the near infrared close to 900 nm of wavelength. The versatility, stability, and high coupling efficiency of this method are promising for quantum optics and sensing experiments in constrained environments, where obtaining high signal-to-noise ratio remains a challenge

Bogoliubov excitations driven by thermal lattice phonons in a quantum fluid of light

Elementary excitations in weakly interacting quantum fluids have a correlated particle-hole nature that leads to spectacular macroscopic quantum phenomena such as superfluidity. This many-body character was established in the context of cold-atom condensates at thermal equilibrium in the framework of Bogoliubov's celebrated theory of the weakly interacting Bose gas. Bogoliubov excitations were also found to be highly relevant to driven-dissipative quantum fluid of light, with certain resulting phenomena strikingly analogue to their equilibrium counterparts, but also genuine out-of-equilibrium aspects. In this work, we investigate both theoretically and experimentally a regime in which the elementary excitations in a quantum fluid of light result dominantly from their interaction with thermal lattice phonons, namely the elementary vibrations of the crystal. By an accurate comparison with the theoretically predicted spectral function of the driven-dissipative quantum fluid we achieve a quantitative understanding of the particle-hole nature of the elementary excitations, and unveil a remarkable decoupling from thermal excitations which is expected to be relevant in equilibrium quantum fluids as well. Finally, we exploit this quantitative understanding to identify a crossover temperature around $1\,$K, below which the lattice phonons are sufficiently quieted down for the quantum fluctuations to take over in the generation of Bogoliubov excitations. This regime is highly desired as it is characterized by strong quantum correlations between Bogoliubov excitations.Comment: Main text: 22 pages 6 figures, Supplementary Information : 4 pages, 3 figure

Explicit Determination of Pinned-Pinned Beams with a Finite Number of Given Buckling Loads

We present an analytical procedure for the exact, explicit construction of Euler-Bernoulli beams with given values of the first N buckling loads. The result is valid for pinned-pinned (P-P) end conditions and for beams with regular bending stiffness. The analysis is based on a reduction of the buckling problem to an eigenvalue problem for a vibrating string, and uses recent results on the exact construction of Sturm-Liouville operators with prescribed natural frequencies

Elliptical micropillars for efficient generation and detection of coherent acoustic phonons

Coherent acoustic phonon generation and detection assisted by optical resonances are at the core of efficient optophononic transduction processes. However, when dealing with a single optical resonance, the optimum generation and detection conditions take place at different laser wavelengths, i.e. different detunings from the cavity mode. In this work, we theoretically propose and experimentally demonstrate the use of elliptical micropillars to reach these conditions simultaneously at a single wavelength. Elliptical micropillar optophononic resonators present two optical modes with orthogonal polarizations at different wavelengths. By employing a cross-polarized scheme pump-probe experiment, we exploit the mode splitting and couple the pump beam to one mode while the probe is detuned from the other one. In this way, at a particular micropillar ellipticity, both phonon generation and detection processes are enhanced. We report an enhancement of a factor of ~3.1 when comparing the signals from elliptical and circular micropillars. Our findings constitute a step forward in tailoring the light-matter interaction for more efficient ultrahigh-frequency optophononic devices.Comment: 10 pages, 5 figure

GaN/Ga2O3 Core/Shell Nanowires Growth: Towards High Response Gas Sensors

International audienceThe development of sensors working in a large range of temperature is of crucial importance in areas such as monitoring of industrial processes or personal tracking using smart objects. Devices integrating GaN/Ga2O3 core/shell nanowires (NWs) are a promising solution for monitoring carbon monoxide (CO). Because the performances of sensors primarily depend on the material properties composing the active layer of the device, it is essential to control them and achieve material synthesis in the first time. In this work, we investigate the synthesis of GaN/Ga2O3 core-shell NWs with a special focus on the formation of the shell. The GaN NWs grown by plasma-assisted molecular beam epitaxy, are post-treated following thermal oxidation to form a Ga2O3-shell surrounding the GaN-core. We establish that the shell thickness can be modulated from 1 to 14 nm by changing the oxidation conditions and follows classical oxidation process: A first rapid oxide-shell growth, followed by a reduced but continuous oxide growth. We also discuss the impact of the atmosphere on the oxidation growth rate. By combining XRD-STEM and EDX analyses, we demonstrate that the oxide-shell is crystalline, presents the β-Ga2O3 phase, and is synthesized in an epitaxial relationship with the GaN-core

Croissance de nanofils InGaN pour les dispositifs de récupération d’énergie photovoltaïques et piézoélectriques

III-nitride materials are excellent semiconductors presenting several interesting properties for photovoltaic and piezoelectric applications. At the same time, the epitaxial growth of these materials in the form of nanowires (NW) is even more interesting, because binary and heterostructured III-N NWs have a higher crystalline quality compared to the 2D and bulk counterparts. In these contexts, this work focuses on the plasma-assisted MBE (PA-MBE) growth of InGaN / GaN NWs and their characterization. Three main topics are addressed: the growth of axial InGaN heterostructures by PA-MBE, their optical characterization, and the study of the selective area growth (SAG) of GaN NWs on transferred graphene. These studies allowed me to obtain a rational control on the growth mode of InGaN heterostructures in a wide range of In contents (up to ~ 40%) and morphologies, to study their axial band edge profile, useful for the optimal design of the photovoltaic structure, and to demonstrate for the first time in the literature, that the SAG of GaN NWs on patterned mono-layer graphene is a possible and very promising strategy to improve their homogeneity. Also, preliminary tests have shown that the piezoelectric conversion capacity of GaN NWs can be improved by about 35% when integrating an In-rich InGaN insertion into their volume.All these results constitute a decisive step in the control and the comprehension of the properties of these nanostructures, and establish very encouraging perspectives for their integration in novel and efficient photovoltaic and piezoelectric nano-generators.Les matériaux III-nitrures sont des excellents semi-conducteurs qui présentent plusieurs propriétés intéressantes pour les applications photovoltaïques et piézoélectriques. Au même temps, la croissance epitaxiale de ces matériaux sous forme de nanofil (NF) est de tant en plus intéressant, car les NFs nitrures binaires et heterostructurés, ont une qualité cristalline supérieure comparés aux homologues 2D et massifs. Dans ces contextes, ce travail est axé sur la croissance par MBE assistée par plasma (PA-MBE) de NFs InGaN/GaN et leur caractérisation. Trois sujets principaux ont été abordés: l'étude de la croissance d’heterostructures InGaN axiales par PA-MBE, leur caractérisation optique, et l'étude de la croissance sélective de NFs GaN sur graphène transféré. Ces études m’ont permis d’obtenir un control rational sur le mode de croissance d’heterostructures InGaN dans une large gamme de teneurs d’In (jusqu'à ~ 40%) et morphologies, de étudier leur structure de bande axiale, utile pour la conception optimale de la structure p-i-n photovoltaïque, et de démontrer pour le première fois dans la littérature, que l’épitaxie sélective de NFs de GaN sur MCG lithographié est une route possible et très promettent pour améliorer leur homogénéité. Ainsi, des tests préliminaires ont montré que la capacité de piézo-conversion des NFs GaN peut être améliorée d'environ 35% lors de l'intégration d’une insertion InGaN riche en In dans leur volume.Tous ces résultats constituent un ’étape décisive dans le contrôle et la comprension des propriétés de ces nanostructures, et donnent des perspectives très encourageantes pour leur intégrations dans des nano-générateurs à haute efficacité

Growth of InGaN nanowires for photovoltaic and piezoelectric energy harvesting

Les matériaux III-nitrures sont des excellents semi-conducteurs qui présentent plusieurs propriétés intéressantes pour les applications photovoltaïques et piézoélectriques. Au même temps, la croissance epitaxiale de ces matériaux sous forme de nanofil (NF) est de tant en plus intéressant, car les NFs nitrures binaires et heterostructurés, ont une qualité cristalline supérieure comparés aux homologues 2D et massifs. Dans ces contextes, ce travail est axé sur la croissance par MBE assistée par plasma (PA-MBE) de NFs InGaN/GaN et leur caractérisation. Trois sujets principaux ont été abordés: l'étude de la croissance d’heterostructures InGaN axiales par PA-MBE, leur caractérisation optique, et l'étude de la croissance sélective de NFs GaN sur graphène transféré. Ces études m’ont permis d’obtenir un control rational sur le mode de croissance d’heterostructures InGaN dans une large gamme de teneurs d’In (jusqu'à ~ 40%) et morphologies, de étudier leur structure de bande axiale, utile pour la conception optimale de la structure p-i-n photovoltaïque, et de démontrer pour le première fois dans la littérature, que l’épitaxie sélective de NFs de GaN sur MCG lithographié est une route possible et très promettent pour améliorer leur homogénéité. Ainsi, des tests préliminaires ont montré que la capacité de piézo-conversion des NFs GaN peut être améliorée d'environ 35% lors de l'intégration d’une insertion InGaN riche en In dans leur volume.Tous ces résultats constituent un ’étape décisive dans le contrôle et la comprension des propriétés de ces nanostructures, et donnent des perspectives très encourageantes pour leur intégrations dans des nano-générateurs à haute efficacité.III-nitride materials are excellent semiconductors presenting several interesting properties for photovoltaic and piezoelectric applications. At the same time, the epitaxial growth of these materials in the form of nanowires (NW) is even more interesting, because binary and heterostructured III-N NWs have a higher crystalline quality compared to the 2D and bulk counterparts. In these contexts, this work focuses on the plasma-assisted MBE (PA-MBE) growth of InGaN / GaN NWs and their characterization. Three main topics are addressed: the growth of axial InGaN heterostructures by PA-MBE, their optical characterization, and the study of the selective area growth (SAG) of GaN NWs on transferred graphene. These studies allowed me to obtain a rational control on the growth mode of InGaN heterostructures in a wide range of In contents (up to ~ 40%) and morphologies, to study their axial band edge profile, useful for the optimal design of the photovoltaic structure, and to demonstrate for the first time in the literature, that the SAG of GaN NWs on patterned mono-layer graphene is a possible and very promising strategy to improve their homogeneity. Also, preliminary tests have shown that the piezoelectric conversion capacity of GaN NWs can be improved by about 35% when integrating an In-rich InGaN insertion into their volume.All these results constitute a decisive step in the control and the comprehension of the properties of these nanostructures, and establish very encouraging perspectives for their integration in novel and efficient photovoltaic and piezoelectric nano-generators

Bogoliubov Excitations Driven by Thermal Lattice Phonons in a Quantum Fluid of Light

The elementary excitations in weakly interacting quantum fluids have a nontrivial nature which is at the basis of defining quantum phenomena such as superfluidity. These excitations and the physics they lead to have been explored in closed quantum systems at thermal equilibrium both theoretically within the celebrated Bogoliubov framework and experimentally in quantum fluids of ultracold atoms. Over the past decade, the relevance of Bogoliubov excitations has become essential to understand quantum fluids of interacting photons. Their driven-dissipative character leads to distinct properties with respect to their equilibrium counterparts. For instance, the condensate coupling to the photonic vacuum environment leads to a nonzero generation rate of elementary excitations with many striking implications. In this work, considering that quantum fluids of light are often hosted in solid-state systems, we show within a joint theory-experiment analysis that the vibrations of the crystal constitute another environment that the condensate is fundamentally coupled to. This coupling leads to a unique heat transfer mechanism, resulting in a large generation rate of elementary excitations in typical experimental conditions, and to a fundamental nonzero contribution at vanishing temperatures. Our work provides a complete framework for solid-embedded quantum fluids of light, which is invaluable in view of achieving a regime dominated by photon-vacuum fluctuations