Intervenção 4

Antes de mais, um elogio aos organizadores deste debate: fazem falta contextos como este, para podermos conversar sobre problemas, situações, ideias, em que de um ou outro modo, estamos todos envolvidos. Agradeço pois o convite para estar aqui. Quereria dirigir-me a todos os pontos propostos no guião que nos enviaram para este debate, mas não há tempo, por isso escolho alguns. – O que aconteceu à roda destes famosos cartoons põe-nos perante o direito à “liberdade de expressão” de todos os se..

Presença e ausência: indícios literários do divino

De modo sumário, este texto mostra como a humanidade ao longo da História manteve viva a pergunta pelo sentido último da existência humana sobre a terra; como culturas e religiões foram dando respostas diversas a essa interrogação, tendo todas elas um carácter provisório enquanto resposta—apesar da existência de revelações religiosas. Por isso essa interrogação fundamental continua a emergir, através de múltiplas vozes, em muitos tempos e lugares, dentro e fora dos quadros espirituais e religiosos existentes. A dimensão interrogativa quanto ao sentido último da vida parece assim surgir com modalidades diferenciadas em quase todos os contextos culturais do mundo. Por exemplo, a literatura, e outras formas de arte, é um dos espaços que incorpora essa busca do Invisível. Através de uma sua afirmação, dúvida, recusa ou mesmo de uma negação, figuram em muitos textos literários preocupações metafísicas e expressões de inquietação acerca do Divino. Em alguns exemplos, da poesia e da ficção narrativa do século XX e do XXI em Portugal, tenta-se aqui observar vários modos como a questão do Divino se inscreve.This text addresses the question of how throughout History mankind has kept alive the quest for ultimate meaning for our existence upon earth. Cultures and religions give different answers to this search. All of them, yet, remain provisional answers, in spite of all religious revelation. Therefore, the question has always kept being asked in many times and places, enacted by multiple voices, inside and outside the actual spiritual or religious frames. This all pervasive interrogative dimension seems thus to emerge in multiple forms from inside all cultural contexts. Literature, for example, as well as other forms of art, is one of the spaces, where signs of this search for the Invisible are present: both by means of affirmation and negation, of refusal or doubt, metaphysical concerns and modes of unquietness about the Divine are present in many literary texts. Focusing on some of the poetry and fictional narrative from the last and the current centuries in Portugal, this paper provides a few examples of how this path for further meaning and for a nameless Divine is dealt with and textually inscribed

Lasing in Si₃N₄-organic hybrid (SiNOH) waveguides

Silicon nitride (Si$_{3}$N$_{4}$) waveguides offer low-loss wave propagation over a wide spectral range including visible wavelengths and lend themselves to photonic integrated circuits for bio-photonic applications. The Si$_{3}$N$_{4}$ device portfolio, however, is so far limited to passive devices that need to be fed by external light sources. This often requires delicate and costly fiber-chip coupling schemes that are subject to stringent alignment tolerances. In this paper, we present and investigate a class of lasers that combine Si$_{3}$N$_{4}$ waveguides with light-emitting organic cladding materials in a hybrid approach. These Si$_{3}$N$_{4}$-organic hybrid (SiNOH) lasers are operated by optical pumping from the top with low alignment precision. We theoretically and experimentally investigate different SiNOH laser concepts based on spiral-shaped ring resonators and distributed feedback (DFB) resonators. While our devices are designed for an emission wavelength of approximately 600 nm, the SiNOH laser concept can be transferred to a large range of wavelengths in the visible spectrum. The devices are amenable to cost-efficient mass production and have the potential to address a wide range of applications in bio-photonics and point-of-care diagnostics

Interpreting the Time-Resolved Photoluminescence of Quasi-2D Perovskites

Optical excitation of quasi-2D perovskites leads to excited-state populations of excitons, free charge carriers, or a mixture of both, depending on the type and amount of 2D spacer used. The fluence dependence of three quantities: 1) the time-resolved photoluminescence decay, 2) the photoluminescence quantum yield (PLQY) after pulsed excitation, and 3) the initial rate of photon emission, allow the mixture of excited states present to be determined. These can be described by a simple model considering noninteracting populations of excitons and charge carriers in separate subvolumes of the film. The model reproduces all unique features of the data, such as the anomalous peak of the PLQY at intermediate fluences, due to bimolecular free carrier emission gaining efficiency before exciton–exciton annihilation reduces the exciton emission efficiency. The excited state population varies from 100% excitons in films made from high concentrations of butylamine spacers to ≈7% excitons and 93% free carriers for low concentrations of 1-naphthylmethylamine spacers. The effective rates of free carrier recombination and exciton–exciton annihilation are high, often on the order of 1 × 10−9 cm3 s−1. The implications for the different excited-state populations and their dynamics in terms of device engineering are discussed

Continuous wave amplified spontaneous emission in phase-stable lead halide perovskites

Sustained stimulated emission under continuous-wave (CW) excitation is a prerequisite for new semiconductor materials being developed for laser gain media. Although hybrid organic-inorganic lead-halide perovskites have attracted much attention as optical gain media, the demonstration of room-temperature CW lasing has still not been realized. Here, we present a critical step towards this goal by demonstrating CW amplified spontaneous emission (ASE) in a phase-stable perovskite at temperatures up to 120 K. The phase-stable perovskite maintains its room-temperature phase while undergoing cryogenic cooling and can potentially support CW lasing also at higher temperatures. We find the threshold level for CW ASE to be 387 W cm-2 at 80 K. These results indicate that easily-fabricated single-phase perovskite thin films can sustain CW stimulated emission, potential at higher temperatures as well, by further optimization of the material quality in order to extend the carrier lifetimes