Generation of Rabi frequency radiation using exciton-polaritons

We study the use of exciton-polaritons in semiconductor microcavities to generate radiation spanning the infrared to terahertz regions of the spectrum by exploiting transitions between upper and lower polariton branches. The process, which is analogous to difference-frequency generation (DFG), relies on the use of semiconductors with a nonvanishing second-order susceptibility. For an organic microcavity composed of a nonlinear optical polymer, we predict a DFG irradiance enhancement of $2.8\cdot10^2$, as compared to a bare nonlinear polymer film, when triple resonance with the fundamental cavity mode is satisfied. In the case of an inorganic microcavity composed of (111) GaAs, an enhancement of $8.8\cdot10^3$ is found, as compared to a bare GaAs slab. Both structures show high wavelength tunability and relaxed design constraints due to the high modal overlap of polariton modes.Comment: 8 pages, 7 figure

Organic Photodiodes with an Extended Responsivity using Ultrastrong Light-Matter Coupling

In organic photodiodes (OPDs) light is absorbed by excitons, which dissociate to generate photocurrent. Here, we demonstrate a novel type of OPD in which light is absorbed by polaritons, hybrid light-matter states. We demonstrate polariton OPDs operating in the ultra-strong coupling regime at visible and infrared wavelengths. These devices can be engineered to show narrow responsivity with a very weak angle-dependence. More importantly, they can be tuned to operate in a spectral range outside that of the bare exciton absorption. Remarkably, we show that the responsivity of a polariton OPD can be pushed to near infrared wavelengths, where few organic absorbers are available, with external quantum efficiencies exceeding those of a control OPD

Optical Nonlinearities in the Strong Light-Matter Coupling Regime

Dans le régime linéaire, deux faisceaux lumineux se traversent sans être perturbés. Cependant, en présence de non-linéarités optiques, de nombreux effets technologiquement intéressants peuvent être observés, tels que la génération de nouvelles fréquences optiques et le contrôle d’un faisceau par un autre. En raison des faibles non-linéarités présentes dans les cristaux optiques, des puissances optiques élevées sont généralement requises pour observer de tels effets non linéaires. Dans certaines applications, telles que la génération de lumière cohérente, le fonctionnement à haute puissance n’est pas problématique. En fait, les techniques de mélange de fréquences et de génération d’harmoniques sont amplement utilisées dans les sources lumineuses commerciales avec des longueurs d’onde d’émission allant de l’ultraviolet profond aux régions infrarouges lointaines du spectre. Il existe toutefois de nombreuses applications en développement dans lesquelles le fonctionnement à faible consommation est essentiel. Dans le domaine du calcul optique, par exemple, des transistors optiques fonctionnant avec des centaines de photons seulement sont nécessaires pour permettre la fabrication de processeurs optiques plus rapides et plus efficaces que les processeurs électroniques. De tels systèmes bénéficieraient également d’une conversion de fréquence à basse puissance afin d’interfacer les signaux optiques de différentes fréquences sur le même circuit photonique. Pour que le fonctionnement à faible puissance devienne possible, de très grandes non-linéarités optiques sont nécessaires. Un système dans lequel les non-linéarités optiques sont si fortes que l’arrivée d’un seul photon peut bloquer la transmission d’un autre est celui d’un seul émetteur quantique placé dans une cavité optique de haute qualité. Les principaux inconvénients de tels systèmes sont leur complexité technologique, leur faible évolutivité et leur fonctionnement à des températures cryogéniques. Dans cette thèse, nous étudions une approche alternative pour améliorer les non-linéarités optiques dans laquelle une collection d’émetteurs est amenée à interagir fortement avec la lumière, créant des quasiparticules lumière-matière appelées exciton-polaritons. Par rapport aux systèmes basés sur des émetteurs uniques, notre approche est plus simple et compatible avec le fonctionnement à température ambiante.----------Abstract In the linear regime, two light beams will go through one another unperturbed. However, in the presence of optical nonlinearities, many technologically interesting effects can be observed, such as the generation of new optical frequencies and the control of one beam by another. Due to the small nonlinearities found in optical crystals, high optical powers are typically required to observe such nonlinear effects. In some applications, such as in coherent light generation, high power operation is not problematic. In fact, frequency mixing and harmonic generation techniques are extensively used in commercial light sources with emission wavelengths ranging from the deep ultraviolet to the far infrared regions of the spectrum. There are, however, many developing applications in which low power operation is critical. In the field of optical computation, for instance, optical transistors operating with only hundreds of photons are required to enable the fabrication of optical processors that are faster and more efficient than electronic ones. Such systems would also benefit from low power frequency conversion in order to interface optical signals of different frequencies to the same photonic circuit. For low power operation to become feasible, very large optical nonlinearities are required. One system in which optical nonlinearities are so strong that the arrival of a single photon can block the transmission of another is that of a single quantum emitter placed inside a high quality optical cavity. The main drawbacks of such a system are their technological complexity, low scalability and operation at cryogenic temperatures. In this thesis, we study an alternative approach to enhancing optical nonlinearities, in which a collection of emitters is made to interact strongly with light, creating mixed light-matter quasiparticles called exciton-polaritons. Compared to systems based on single emitters, our approach is of simpler implementation and is compatible with room-temperature operation. Under resonant excitation, polaritons interact strongly through their excitonic component and have allowed for the demonstration of a number of nonlinear effects at room temperature. After reviewing the main properties of exciton polaritons, we investigate different ways in which polariton nonlinearities can be used for frequency mixing and harmonic generation, as well as for implementing novel nonlinear devices based on interacting polariton fluids. In the first case, we consider systems in which the excitonic material embedded in a planar microcavity has a large second- or third-order optical nonlinearity

Super-resolved FRET imaging by confocal fluorescence-lifetime single-molecule localization microscopy

FRET-based approaches are a unique tool for sensing the immediate surroundings and interactions of (bio)molecules. FRET imaging and FLIM (Fluorescence Lifetime Imaging Microscopy) enable the visualization of the spatial distribution of molecular interactions and functional states. However, conventional FLIM and FRET imaging provide average information over an ensemble of molecules within a diffraction-limited volume, which limits the spatial information, accuracy, and dynamic range of the observed signals. Here, we demonstrate an approach to obtain super-resolved FRET imaging based on single-molecule localization microscopy using an early prototype of a commercial time-resolved confocal microscope. DNA Points Accumulation for Imaging in Nanoscale Topography (DNA-PAINT) with fluorogenic probes provides a suitable combination of background reduction and blinking kinetics compatible with the scanning speed of usual confocal microscopes. A single laser is used to excite the donor, a broad detection band is employed to retrieve both donor and acceptor emission, and FRET events are detected from lifetime information

On the possibility of a terahertz light emitting diode based on a dressed quantum well

We consider theoretically the realization of a tunable terahertz light emitting diode from a quantum well with dressed electrons placed in a highly doped p-n junction. In the considered system the strong resonant dressing field forms dynamic Stark gaps in the valence and conduction bands and the electric field inside the p-n junction makes the QW asymmetric. It is shown that the electrons transiting through the light induced Stark gaps in the conduction band emit photons with energy directly proportional to the dressing field. This scheme is tunable, compact, and shows a fair efficiency.Comment: 6 pages, 5 figure

Manipulating molecules with strong coupling: harvesting triplet excitons in organic exciton microcavities

Exciton-polaritons are quasiparticles with mixed photon and exciton character that demonstrate rich quantum phenomena, novel optoelectronic devices and the potential to modify chemical properties of materials. Organic semiconductors are of current interest for their room-temperature polariton formation. However, within organic optoelectronic devices, it is often the 'dark' spin-1 triplet excitons that dominate operation. These triplets have been largely ignored in treatments of polariton physics. Here we demonstrate polariton population from the triplet manifold via triplet-triplet annihilation, leading to polariton emission that is longer-lived (>microseconds) even than exciton emission in bare films. This enhancement arises from spin-2 triplet-pair states, formed by singlet fission or triplet-triplet annihilation, feeding the polariton. This is possible due to state mixing, which -in the strong coupling regime- leads to sharing of photonic character with states that are formally non-emissive. Such 'photonic sharing' offers the enticing possibility of harvesting or manipulating even states that are formally dark

Highly nonlinear trion-polaritons in a monolayer semiconductor

Highly nonlinear optical materials with strong effective photon-photon interactions are required for ultrafast and quantum optical signal processing circuitry. Here we report strong Kerr-like nonlinearities by employing efficient optical transitions of charged excitons (trions) observed in semiconducting transition metal dichalcogenides (TMDCs). By hybridising trions in monolayer MoSe2 at low electron densities with a microcavity mode, we realise trion-polaritons exhibiting significant energy shifts at small photon fluxes due to phase space filling. We find the ratio of trion- to neutral exciton–polariton interaction strength is in the range from 10 to 100 in TMDC materials and that trion-polariton nonlinearity is comparable to that in other polariton systems. The results are in good agreement with a theory accounting for the composite nature of excitons and trions and deviation of their statistics from that of ideal bosons and fermions. Our findings open a way to scalable quantum optics applications with TMDCs

O ensino da escrita representado em textos produzidos por professores após um processo de formação continuada

Orientação: Profa. Dra. Adriana Cintra de Carvalho PintoDissertação (Mestrado em Lingüística Aplicada) - Departamento de Ciências Sociais e Letras, Universidade de Taubaté, Taubaté, 2015.Made available in DSpace on 2019-07-26T19:20:17Z (GMT). No. of bitstreams: 1 Gisele Maria Souza Barachati.pdf: 1753160 bytes, checksum: d9167ff93d79296c7e2e9e1b87f1f72d (MD5) Previous issue date: 2015Resumo: Esta pesquisa de mestrado tem como tema central as representações de professores sobre a tarefa de ensinar a escrever. Inserido em um processo de formação continuada, esse profissional constrói representações sobre seu trabalho, que podem ou não interferir em seu agir em sala de aula. Partindo-se dessa premissa, esse trabalho visa a identificar e analisar as representações do ensino da escrita, configuradas em um texto produzido por uma professora do Ensino Fundamental I, após um percurso de formação continuada. Essa pesquisa desenvolveu-se com base nos aportes teóricos do Interacionismo Sociodiscursivo (ISD) e contribuições da Clínica da Atividade (metodologia da Instrução ao Sósia). Foi analisado, qualitativamente, o texto oral de uma professora de Anos Iniciais, de uma Rede Municipal de Ensino no interior do Estado de São Paulo, que participou de dez horas de oficinas dedicadas ao estudo de práticas metodológicas de ensino da produção textual para crianças de seis a onze anos de idade. Sintetizando-se os resultados obtidos pode-se concluir que as representações da professora sobre seu métier, especialmente sobre a tarefa de ensinar a escrever, reconfiguradas em seu texto, revelam a escrita como um conteúdo complexo de ensinar, cuja responsabilidade recai sobre o professor, agente dotado de intenções, motivos e finalidades. O ensino da escrita, pela complexidade que se apresenta, é representado pela professora na forma de uma sequência didática, por ser tratar de um processo de construção de conhecimento que requer a realização de diversas etapas de ensino até se chegar à escrita dos alunos, propriamente dita. Essas representações sobre o ensino da escrita são oriundas de um longo processo de apropriação e reapropriação dessa tarefa, tanto a partir dos modelos do agir existentes na sociedade - o gênero de atividade, o agir dos formadores no processo de formação continuada e de outros professores ? quanto das representações sociais do trabalho do professor e aquelas expressas em textos sobre, por e para o profissional da educação. Esse trabalho pode contribuir aos formadores de professores para que, a partir dessas representações sobre o ensino da escrita, compreendam melhor suas ações na formação docente e o processo de apropriação e reapropriação pelo qual passa o professor, ao longo de toda a sua carreira profissional, não reproduzindo aquilo que vivencia, mas modificando seu agir enquanto agente de sua própria prática pedagógica. À comunidade científica, especialmente os grupos de pesquisa, cujo embasamento teórico é o Interacionismo Sociodiscursivo e a Clínica da Atividade, esta pesquisa contribui com uma melhor compreensão do trabalho do professor, em especial o ensino da escrita, a partir da análise de um texto produzido pelo próprio profissional. Em relação à metodologia de coleta de dados, a Instrução ao Sósia, essa pesquisa também traz a sua contribuição no sentido de servir ao ISD como forma de coleta indireta de dados, fazendo com que o professor, ao falar do trabalho do outro, revele representações de seu próprio agir.Abstract: This research has as central theme the representations of teachers about the task of teaching young learners how to write. Within a process of continued teaching formation, the teacher elaborates representations of his work, which can or cannot interfere in his actions in the classroom. Starting from this assumption, this academic paperwork aims to identify and analyze the representations of the teaching of writing skills, configured in a text produced by a Fundamental Education teacher, after being part of a process of teaching formation. This research was developed based on the Sociodiscursive Interactionism conception (ISD) and contributions of the Clinic of the Activity (the lookalike's instruction procedure). An oral text, from a Fundamental Education teacher, of a public group of schools, in a city in the state of São Paulo, was analyzed, qualitatively, after being part of a ten hour teaching formation about methodologies of writing skill teaching for children from six to eleven years old. A brief view of the results of this research leads us to the conclusion that the teacher representations of his métier, specially the task of teaching how to write, reconfigured in his text, reveals the writing skill as a complex content of teaching, whose responsible is the teacher himself, an agent with intentions, motives and goes. The teaching of writing skills, for its complexity, is represented by the teacher as a sequence of activities and as a process of learning which presumes the realization of many teaching stages until the children can write a text themselves. These representations about writing skill teaching come from a long process of appropriation and (re)appropriation of this task, from a series of social preexisting acting models – the activity genre, the actions of the teacher's teachers in the encounters of teaching formation and the acting of other professional colleagues – social representations of the educational profession and also representations from texts about, from and for this professional. This academic paperwork can be a contribution to the professionals who teach the teachers, for them to consider the representations teachers have about the task to teach writing skills, as a way to have a better understanding of the educational professionals and the process which they are involved to appropriate and (re)appropriate this task, for as long as his career can accomplish and not just a process of repeating other actions, but developing his own. To the scientific community, especially to the research groups which take de conception of the Sociodiscursive Interactionism and the Clinic of the Activity as basis for their research, this paperwork can contribute to a deeper understanding of the teachers’ work, from the analyses of his own text. The methodology of collecting data, the lookalike's instruction procedure, is also a contribution from this research as an indirect form of data collection which makes the teacher talks about other's work, not knowing that he is talking about the representations of his own actions.Mestrad