1,721,030 research outputs found
On long-range plasmonic modes in metallic gaps
No full textSatuby and Orenstein [Opt. Express 15, 4247-4252 (2007)] reported the discovery and numerical and experimental investigation of long-range surface plasmon-polariton eigenmodes guided by wide (6 to 12 micrometer) rectangular gaps in 400 nm thick gold films using excitation of vacuum wavelength lambda = 1.55 micrometer. In this paper, we carry out a detailed numerical analysis of the two different types of plasmonic modes in these structures. We show that no long-range eigenmodes exists for these gap plasmon waveguides, and that the reported "modes" are likely to be beams of bulk waves and surface plasmons, rather than guided modes of the considered structures
Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation
Get PDFHigh-refractive index nanostructured dielectrics have the ability to locally enhance electromagnetic fields with low losses while presenting high third-order nonlinearities. In this work, we exploit these characteristics to achieve efficient ultrafast all-optical modulation in a crystalline gallium phosphide (GaP) nanoantenna through the optical Kerr effect (OKE) and two-photon absorption (TPA) in the visible/near-infrared range. We show that an individual GaP nanodisk can yield differential reflectivity modulations of up to -40%, with characteristic modulation times between 14 and 66 fs, when probed at the anapole excitation (AE). Numerical simulations reveal that the AE represents a unique condition where both the OKE and TPA contribute with the same modulation sign, maximizing the response. These findings highly outperform previous reports on sub-100-fs all-optical switching from resonant nanoscale dielectrics, which have demonstrated modulation depths no larger than 0.5%, placing GaP nanoantennas as a promising choice for ultrafast all-optical modulation at the nanometer scale.Fil: Grinblat, Gustavo Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Zhang, Haizhong. Institute of Materials Research and Engineering; SingapurFil: Nielsen, Michael P.. University of New South Wales; AustraliaFil: Krivitsky, Leonid. Institute of Materials Research and Engineering; SingapurFil: Berté, Rodrigo. Ludwig Maximilians Universitat; AlemaniaFil: Li, Yi. Ludwig Maximilians Universitat; AlemaniaFil: Tilmann, Benjamin. Ludwig Maximilians Universitat; AlemaniaFil: Cortés, Emiliano. Ludwig Maximilians Universitat; AlemaniaFil: Oulton, Rupert F.. Imperial College London; Reino UnidoFil: Kuznetsov, Arseniy I.. Institute of Materials Research and Engineering; SingapurFil: Maier, Stefan A.. Ludwig Maximilians Universitat; Alemani
Semiconductor nanoplasmonics
Get PDFThe weak optical nonlinearities of natural materials restrict device sizes in photonic integrated circuits to dimensions far larger than conventional electronics. By exploiting the strong coupling between photons and collective electron oscillations in metals, plasmonics can confine light far below the Abbe diffraction limit. This increased confinement leads to enhanced nonlinear interactions that can be used for a wide range of applications. This thesis examines the integration of plasmonic components into semiconductor photonic architectures in order to utilize the strong light-matter interactions inherent in plasmonics to improve the performance of photonic integrated circuits.
In order to study integrated plasmonic devices, free-space laser light must first be coupled into the optical devices. To this end, a directional plasmonic-photonic coupler was designed to efficiently couple ultrashort pulses on-chip. Then, silicon hybrid gap plasmon waveguides (HGPWs) were studied for their waveguiding properties which includes the transition from photonic-like to plasmonic-like properties depending on gap width. Three-photon absorption photoluminescence in selectively deposited quantum dots showed the viability of these waveguides for extreme nanofocusing, which can be used to enhance light-matter interactions.
With the capability for high light intensities comes the possibility of nonlinear applications such as frequency mixing in the HGPWs. Four-wave mixing (FWM) in these waveguides was thus first explored theoretically and found to be promising, with conversion efficiencies comparable to photonic devices, and with no reliance upon phase-matching or dispersion considerations. The Z-scan measurement technique was utilized to explore organic polymers for the high nonlinearity and low refractive index necessary for plasmonics. Solution processing of such films is also advantageous for integrating the nonlinear material within nanoscopic gaps. Finally, once a suitable nonlinear polymer was found, FWM in the HGPWs was explored experimentally. These findings give further evidence of the capabilities of plasmonics to enable strong light-matter interactions in extremely small volumes.Open Acces
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Giant and Tunable Optical Nonlinearity in Single‐Crystalline 2D Perovskites due to Excitonic and Plasma Effects
No full textMaterials with large optical nonlinearity, especially in the visible spectral region, are in great demand for applications in all-optical information processing and quantum optics. 2D hybrid Ruddlesden−Popper-type halide perovskites (RPPs) with tunable ultraviolet-to-visible direct bandgaps exhibit large nonlinear optical responses due to the strong excitonic effects present in their multiple quantum wells. Using a microscopic Z-scan setup with femtosecond laser pulses tunable across the visible spectrum, it is demonstrated that single-crystalline lead halide RPP nanosheets possess unprecedentedly large nonlinear refraction and absorption coefficients near excitonic resonances. A room-temperature insulator (exciton)–metal (plasma) Mott transition is found to occur near the exciton resonance of the thinnest qunatum-well RPPs, boosting the nonlinear response. Owing to the rapidly changing refractive index near resonance, a single RPP crystal can exhibit different nonlinear functionalities across the excitation spectrum. The results suggest that RPPs are efficient nonlinear materials in the visible waveband, indicating their potential use in integrated nonlinear photonic applications such as optical modulation and switching.Fil: Abdelwahab, Ibrahim. Imperial College London; Reino Unido. National University Of Singapore; SingapurFil: Dichtl, Paul. Imperial College London; Reino UnidoFil: Grinblat, Gustavo Sergio. Imperial College London; Reino UnidoFil: Leng, Kai. National University Of Singapore; SingapurFil: Chi, Xiao. National University Of Singapore; SingapurFil: Park, In-Hyeok. National University Of Singapore; SingapurFil: Nielsen, Michael P.. Imperial College London; Reino UnidoFil: Oulton, Rupert F.. Imperial College London; Reino UnidoFil: Loh, Kian Ping. National University Of Singapore; SingapurFil: Maier, Stefan A.. Imperial College London; Reino Unid
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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