1,720,959 research outputs found
Multilayer Hyperbolic Metamaterials for Tunable Nanophotonics Applications
No full textMaterials with reconfigurable optical properties and possessing the ability to actively manipulate light at the nanoscale are among the greatest requirements of advanced nanophotonics and quantum optics. In particular, the enhancement and the control of optical nonlinearities and quantum emitters photoluminescence represent a fundamental challenge for the development of many optoelectronic devices for all-optical signal processing in integrated photonic circuits. In recent years, the scientific and technological research has strongly pursued the development of novel nanocomposites with peculiar optical properties that are absent in natural materials, and derive from the tailoring of their geometrical and compositional features by subwavelength nanofabrication. These are called metamaterials, taking their name from the ancient greek Mετα ("meta"), which means "beyond". Indeed, their properties go beyond the conventional ones in nature. In this framework, hyperbolic metamaterials (HM) stand out among the most promising cutting-edge nanomaterials owing to their epsilon-near-zero (ENZ) properties and their unique hyperbolic dispersion. These originate from the combination of constituent materials with opposite optical features (i.e. a metal and a dielectric) in a structural design bringing forth to an extreme uniaxial anisotropy of the effective permittivity (whose real part goes to zero at the ENZ wavelength), and a potentially unlimited photonic density of states. Strong optical nonlinearities and enhancement of the radiative decay rate of quantum light emitters can be obtained owing to these properties, which can be finely engineered across the optical spectrum by geometry and composition, or tuned by external parameters, thus achieving an active control of the phenomena deriving from them. Therefore, HM have great potential to be employed for applications in several fields, ranging from nonlinear nanophotonics to biosensing.
The aim of the present work is the investigation of the tunability of the linear and nonlinear optical properties in multilayer HM by structure design and by external parameters, and the ability of these materials to control the photoluminescence of quantum emitters. To this purpose, hyperbolic multilayers with different metal filling fraction, layers thickness and composition are fabricated. The effective permittivity and the linear optical properties of the produced samples are shown to be tailorable by changing the metal filling fraction via the layers thickness, strictly dependent on plasmonic effects arising from the coupling of surface plasmon polaritons (SPP) sustained at the metal-dielectric interfaces, and controllable by light incidence angle and polarization. The tuning of the optical Kerr effect via the metal filling fraction (i.e. spectrally shifting the ENZ wavelength) is evidenced. A continuous modulation of the nonlinear optical response as a function of the incidence angle with TE- and TM-polarized light is demonstrated around the ENZ wavelength, and a phenomenological model is implemented to simulate the angle and polarization-dependent nonlinear parameters accounting for the optical anisotropy of the HM and the local intensity enhancement inside them. The intensity dependence of the nonlinear optical response is studied. A figure of merit is defined to optimize the multilayer structure and composition, and take full advantage of the local intensity enhancement favoured by the SPP coupling in the ENZ regime for boosting the nonlinear optical response. Finally, a selective control of specific transitions of Eu3+ emitters coupled to hyperbolic multilayers is pointed out in their hyperbolic regime, and by changing the distance from them. The obtained results highlight multilayer HM as potential platforms for all-optical switches, optical limiters, single-photon sources and nanolasers.Materials with reconfigurable optical properties and possessing the ability to actively manipulate light at the nanoscale are among the greatest requirements of advanced nanophotonics and quantum optics. In particular, the enhancement and the control of optical nonlinearities and quantum emitters photoluminescence represent a fundamental challenge for the development of many optoelectronic devices for all-optical signal processing in integrated photonic circuits. In recent years, the scientific and technological research has strongly pursued the development of novel nanocomposites with peculiar optical properties that are absent in natural materials, and derive from the tailoring of their geometrical and compositional features by subwavelength nanofabrication. These are called metamaterials, taking their name from the ancient greek Mετα ("meta"), which means "beyond". Indeed, their properties go beyond the conventional ones in nature. In this framework, hyperbolic metamaterials (HM) stand out among the most promising cutting-edge nanomaterials owing to their epsilon-near-zero (ENZ) properties and their unique hyperbolic dispersion. These originate from the combination of constituent materials with opposite optical features (i.e. a metal and a dielectric) in a structural design bringing forth to an extreme uniaxial anisotropy of the effective permittivity (whose real part goes to zero at the ENZ wavelength), and a potentially unlimited photonic density of states. Strong optical nonlinearities and enhancement of the radiative decay rate of quantum light emitters can be obtained owing to these properties, which can be finely engineered across the optical spectrum by geometry and composition, or tuned by external parameters, thus achieving an active control of the phenomena deriving from them. Therefore, HM have great potential to be employed for applications in several fields, ranging from nonlinear nanophotonics to biosensing.
The aim of the present work is the investigation of the tunability of the linear and nonlinear optical properties in multilayer HM by structure design and by external parameters, and the ability of these materials to control the photoluminescence of quantum emitters. To this purpose, hyperbolic multilayers with different metal filling fraction, layers thickness and composition are fabricated. The effective permittivity and the linear optical properties of the produced samples are shown to be tailorable by changing the metal filling fraction via the layers thickness, strictly dependent on plasmonic effects arising from the coupling of surface plasmon polaritons (SPP) sustained at the metal-dielectric interfaces, and controllable by light incidence angle and polarization. The tuning of the optical Kerr effect via the metal filling fraction (i.e. spectrally shifting the ENZ wavelength) is evidenced. A continuous modulation of the nonlinear optical response as a function of the incidence angle with TE- and TM-polarized light is demonstrated around the ENZ wavelength, and a phenomenological model is implemented to simulate the angle and polarization-dependent nonlinear parameters accounting for the optical anisotropy of the HM and the local intensity enhancement inside them. The intensity dependence of the nonlinear optical response is studied. A figure of merit is defined to optimize the multilayer structure and composition, and take full advantage of the local intensity enhancement favoured by the SPP coupling in the ENZ regime for boosting the nonlinear optical response. Finally, a selective control of specific transitions of Eu3+ emitters coupled to hyperbolic multilayers is pointed out in their hyperbolic regime, and by changing the distance from them. The obtained results highlight multilayer HM as potential platforms for all-optical switches, optical limiters, single-photon sources and nanolasers
Tunable Third-Order Nonlinear Optical Response in ε-Near-Zero Multilayer Metamaterials
No full textMetamaterials with properly engineered linear and nonlinear optical response are of great interest for many advanced applications in nanophotonics and quantum optics. In the present work, we perform a detailed spectral investigation of the third-order nonlinear optical properties (nonlinear refractive index
and nonlinear absorption coefficient) of epsilon-near-zero Au/Al2O3 multilayer metamaterials in a broad range of the visible spectrum across their epsilon-near-zero (ENZ) wavelength, at different incidence angles with TE and TM-polarized light. Multilayers with different gold filling fractions (16 and 33%) are produced by magnetron sputtering to tune the spectral position of the -near-zero wavelength. The results demonstrate that a continuous modulation of the linear and nonlinear optical parameters of these metamaterials can be obtained as a function of the angle of incidence, with a peak of the nonlinear optical coefficients close to the ENZ wavelength. A model is proposed to describe the nonlinear optical response of the metamaterials, and an optimal agreement between experimental and simulated results is obtained in all the configurations explored. This model represents a useful tool to design multilayer metamaterials with tailored nonlinear optical properties, to be used in different experimental configurations
Spectral Nonlinear Optical Response of Ion-Implanted Au and Ag Nanoparticles in Sapphire: A Three-Level Model Description
Full text linkNonlinear materials are of great technological interest for the realization of nanophotonic devices able to control and manipulate light. These properties can be specifically engineered by exploiting the surface
plasmon resonance of plasmonic nanocomposites, in proximity of which nonlinear absorption and refraction are largely enhanced. An exploration of the spectral, irradiance, and host material dependence of the
nonlinear parameters is important to be able to gain a thorough understanding of the nonlinear response. In the present work, we investigate the nonlinear optical response of Au and Ag nanoparticles embedded
in sapphire by a spectral z-scan characterization across the localized surface plasmon band of the samples. We also present a comparison of the results obtained for Au nanoparticles embedded both in silica and in
sapphire, produced under equivalent conditions, to test the influence of the host material. We theoretically describe the spectral trends of both the nonlinear absorption coefficient and nonlinear refractive index by
implementing a three-level model, which provides important insights into the main physical parameters controlling the observed spectral features, and the possibility of ab initio composite designs with tailored properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Selective Control of Eu3+ Radiative Emission by Hyperbolic Metamaterials
Full text linkIn recent years the quest for novel materials possessing peculiar abilities of manipulating light at the nanoscale has been significantly boosted due to the strict demands of advanced nanophotonics and quantum technologies. In this framework radiative decay engineering of quantum emitters is of paramount importance for developing efficient single-photon sources or nanolasers. Hyperbolic metamaterials stand out among the best cutting-edge candidates for photoluminescence control owing to their potentially unlimited photonic density of states and their ability to sustain high-k modes that allow us to strongly enhance the radiative decay rate of quantum light emitters. The aim of the present paper is to show how Au/Al2O3 hyperbolic multilayers can be used to selectively control the photoluminescence of coupled Eu3+ emitters. We point out an enhancement of the Eu3+ transitions when they are in the hyperbolic regime of the metamaterials and a significant alteration of the ED and MD branching ratios by changing the emitter–metamaterial distance
- …
